Frequently Asked Questions

As per standards laid down by the CPHEEO (Central Public Health Environmental & Engineering Organization), the fresh water consumption per day per person should be between 135 to 150 liters per day. It is officially expressed as “liters per capita daily” (lpcd). By and large public water supply and sewerage bodies/authorities all across the country use the former figure to work out probable water consumption.
Waste generation in a residential complex: When water is consumed by people living in a residential complex without access to an underground sewerage/drainage system, the amount consumed is estimated to be 135 lpcd. The total quantity (No. of residents X 135 liters) comes into a sewage treatment plant (STP) in the premises, and this total volume has to be treated by the STP. In a vast majority of cases, the actual waste generated exceeds this figure comfortably leading to overloading of the STP. This happens routinely because almost all residential complexes do not install water meters or similar water volume and flow measurement devices to keep track of water consumption in a residential complex/ gated community. Consequently, when a device is installed and readings monitored, consumption has been found to be double and sometimes triple the suggested figure of 135 lpcd.
Waste generation in a commercial complex: Human occupation of this kind of building is only during “duty hours”,i..e for approximately 8 to 10 hours per shift if there is more than a single shift. In this case water consumption is considered as 50 lpcd per person per shift.

Wastewater contains all the dissolved minerals present in the freshwater that was used and which became waste water as well as all the other contaminants mentioned above. These are proteins, carbohydrates, oils & fats. These contaminants are degradable and use up oxygen in the degradation process. Therefore, these are measured in terms of their demand for oxygen which can be established by certain tests in a laboratory. This is called BioDegradable Oxygen demand (BOD). Some chemicals which also contaminate the water during the process of domestic use also degrade and use oxygen and the test done to establish this demand is called Chemical Oxygen demand (COD). Typically a domestic sewage would contain approximately 300 to 450 mg/litre of BOD and COD on an average. Sewage also contains coliform bacteria (e coli) which is harmful to human beings if water containing such bacteria is consumed (drunk). E coli is bacteria that thrives in the intestines of warm blooded creatures such as humans, animals and birds. Another feature of sewage is the high level of Total Suspended Solids (TSS). This is what gives the sewage a black colour, hence the name “black water”. If sewage is allowed to turn septic, it then also has a strong, unpleasant odour.

Much of the water used for domestic purposes does not require potable (suitable for drinking) water quality. For instance, water used for flushing toilets or for washing floors, yards or roads & gardening does not require to be potable. In a scenario where fresh water is getting increasingly scarce and when enormous volumes of sewage generated in the country are not being treated, but goes unchecked to pollute fresh water from lakes, rivers and the groundwater table, it must be treated. Discharging untreated sewage into any drains other than an underground sewerage system, or into open land, is an offence and invites prosecution under the laws of all Pollution Control Boards in the country. Sewage must necessarily be treated correctly and then reused/recycled for various uses that do not need potable water quality. Recycling/reusing treated sewage can reduce fresh water requirements substantially, by almost 50-60%. In a scenario where fresh water availability itself is increasingly in doubt this is critical.

This requires plumbing to be laid so as to serve two sets of storage tanks on the roofs of any residential/commercial building. One set of storage tanks will be used to receive and store fresh water which will flow through plumbing laid to take it to bathrooms and kitchens where it can be used for drinking, cooking, washing & bathing. The second set of tanks will receive treated sewage which will be connected by plumbing to all the flush tanks in toilets and to other points where the water can be used for washing yards, floors and also for gardening.

Sullage (grey water) which is mentioned above, if collected in a storage tank separately can be treated by aerating it to prevent it from turning septic, and then dosed with a coagulant, chlorinated and then subjected to filtration by pressure sand filtration followed by activated carbon filtration and stored in a separate overhead tank or tanks from which it can be used for flushing toilets and other uses where fresh or potable water is not required. However, the current practice is to combine sullage and sewage (black water) and treat the mixture in an STP (Sewage treatment plant). This practice has come in predominantly to reduce the cost of construction of two separate plants and because space is now at a premium in any building.

From the point of view of a resident it is worth considering as it enhances the water security of the resident. A builder’s priority is totally different, since the space taken up by the treatment system cannot be ‘sold’ to a buyer, he will just not consider it, and instead the builder will combine greywater with sewage in an STP. This enables the builder to save costs. However if looked at from the residents’ view point, a separate grey water treatment system being easier to operate provides a facility to ‘fall back on’ when the STP fails. Why STPs fail becomes clearer as you read on.

Treatment of sewage is based on a method provided by nature, i.e. by using microbial action. When a steady consistent supply of air is pumped into a tank containing sewage which has been screened to remove all floating debris and non-soluble contents in sewage, microbes which are present in it get activated. These microbes are present in the sludge which makes up a substantial part of sewage, and they consume the pollutants in the sewage while the air supply brings them to life and keeps them alive and multiplying. This is a time tested system called the world over as the 'Activated Sludge Process (ASP)'. It is the oldest system worldwide and is the most used process world over. An STP based on this
aerobic process will consist of the following major stages of treatment:
• Primary Treatment: In this stage, raw sewage is screened to remove floating debris/ insoluble impurities such as plastic bags, leaves, twigs, papered.
• Secondary Treatment: In this stage, oxygen (air) is mixed into the sewage to activate the microbes which consume the pollution load and which then become sludge (biomass). Aerated sewage and sludge are then separated so that the sludge can be removed and de-watered/ dried for disposal. The sludge can be used as compost in a garden. The water free from sludge is sent to a clear water tank (also called clarified water tank).
• Tertiary Treatment: Clarified water is filtered through a pressure sand filter and an activated sand filter to remove any remaining suspended impurities and a substantial portion of the BOD & COD present in it. Finally it is disinfected to kill all the bacteria present in it by either chlorination or ozonation or with ultra violet light. This tertiary treated water is then pumped into a dedicated set of storage tanks from where it is used to flush toilets, wash roads, yards and for gardening. A majority of the STPs in India are based on this ASP system in its most basic form. Such STPs are highly susceptible to input fluctuations (a frequent feature in India) and this results in a lot of untreated sewage and other related problems.
Other processes available:
● A fairly recent system called the MBR system (membrane bioreactor system) which is a superior system is becoming very popular. It is a very compact waste treatment system that combines biological decomposition with membrane separation of the sludge (biomass).The membrane compacts & concentrates the sludge making for a far more compact design than the ASP system described above(it combines the secondary and tertiary treatment in one single step). Further it produces far less sludge too. Best of all,it is not so sensitive to input load fluctuations like the ASP system. However, an MBR system requires skilled operators, though it can be automated to cut out operator error and poor
● Reed Bed Sewage Treatment System is an extremely eco friendly system where sewage is allowed into a constructed water body where certain kinds of aquatic plants are planted which absorb atmospheric oxygen and let this out through their roots thereby
providing the oxygen to feed the microbes which will clean up the sewage. This system does however require a tertiary treatment system if the treated sewage is required for anything more than gardening. Its drawback is that it requires a lot of land to function and this is a major disadvantage in a world where space is at a premium. One major advantage is that it requires virtually no electricity to operate if the flow of raw and treated sewage is by

The aerobic process as explained above is one where the microbes which clean up the sewage need to be supplied with air(oxygen) to function and multiply so that the sewage is ‘cleaned up’. An anaerobic process is one where a different kind of bacteria comes into action. It is a bacteria/microbe that does not need air and operates in an atmosphere without air (hence the term ‘anaerobic’).This kind of bacteria produces methane and in the waste/environmental engineering industry, they are called “methanogens”.
Mostly, anaerobic treatment is usually followed by the aerobic process and this combination is used where the waste water has very high values of BOD and COD. In such situations, the anaerobic system reduces the BOD & COD down to a level where the aerobic process completes the job of reducing it down to the levels where a tertiary treatment stage can do the final ‘polishing’ of the treated sewage as stated above.

The most common problems encountered are listed below and are based on an informal survey of STPs (including Water Treatment plants also) carried out over the last 4 years.
● Initial Startup of an STP failing to treat sewage: An STP is normally designed for the total sewage that can be expected when a building or premises is fully occupied. Full occupation in most cases usually takes up to a year or more. During this period when occupancy can be as low as 30% or so and gradually increases over a year or more, consequently the sewage that comes in initially does not provide the minimum load needed for satisfactory operation of an STP. It results in a situation which can only be called “sewage in sewage out”. Many STPs which face this situation take a long time to stabilize and provide treated sewage, very often, due to poor or wrong operation, STPs do not stabilize.
● Poor design/under design of the STP : Often STPs which initially ‘struggle’ to overcome the first problem described above also cannot function because
1. the balancing tank is undersized
2. aeration tank is undersized or clarifier is badly designed
3. The total inflow of sewage is higher than the volume the STP was designed to handle.
The tanks mentioned in 1) & 2) above are part of the primary and secondary treatment portions of an ASP system.
● Consistent mal-operation of the STP: Another very common feature is that a majority of plant operating personnel employed by agencies that take on Operation & Maintenance (O&M) contracts are illiterate, untrained and supervised by people with little or no knowledge of what O&M involves. Such agencies generally charge O&M charges that residents’ associations consider affordable. Companies with well-trained operation personnel and experienced supervisory staff charge for services an amount that reflect their skill and expertise which residents’ Associations are reluctant to pay and thereby lose out on a well-run/operated water infrastructure. They often do not realize that even the charges which they consider as cheaper/lower are going to waste if the sewage is only partially treated.
● Strong smell/odour from the STP: This is a very common complaint from numerous housing communities and even commercial buildings which have an STP in operation. The smell is often very strong and quite often unbearable. It is caused by any one or all of the problems listed above.
● Very high noise levels from the STP: Quite often residents of an apartment building have sought help from experts to minimize the very high noise levels from their STP which they find unbearable throughout the day and more so at night, thereby preventing the residents from sleeping in peace.

● Modern designs for STPs which are modular are available from reputed companies which are in the field of water and wastewater treatment. Such companies have standardized designs where, for instance an STP to handle 150 KLD ( 150,000 Liters per day) of sewage can be made up of 3 modular STPs each of 50KLD capacity. Such an installation would be able to handle the initial lower load of sewage with one module in operation with remaining modules being commissioned/started up as the sewage volume increases. Such a modular approach also makes it possible to handle sewage in the case of a break-down of the STP as it is extremely rare for all modules to break-down together. In short, there is a stand-by always available. For several years now a few companies have been offering microbial agents which can help overcome these problems if these microbial agents are added to the incoming sewage. Go in for Modular STPs & use microbial agents regularly.
● It is equally important to know and be able to control the volume of fresh water used in a community so that it does not exceed the design capacity of an STP. This involves installing water meters at all crucial points to measure water flow (consumption) & thereafter taking action to curb excess consumption of fresh water to prevent overloading the STP. Control excess consumption of fresh water and thereby prevent overloading of the STP
● Builders are not expected to be experts in water or sewage treatment plant design, manufacture etc. They can however have tie-ups with reputed environmental engineering companies with sound technical experience and a proven track record, to make up for their lack of knowledge. This seldom happens since a builder’s interest ends with selling a completed project and then handing over the project to the Resident’s Association as soon as possible, often without even demonstrating actual, successful operation of the water infrastructure. Most builders link up with small, obscure local companies with inadequate knowledge and expertise in waste and water treatment, but will put up something for an extremely low price. The result is poor/ wrong operation of an STP leading to untreated sewage and unpleasant odours from it. Ensure supply of an STP from a reputed supplier and entrust operation & maintenance to a well trained professional team.
● One of the major reasons for STPs not working properly is the fluctuations in input loads. Flow of sewage in a residential community is never uniform. It varies with peak flows in the morning (residents getting ready to go to work), very low or almost no flows later in the day with another peak in the evening. Raw sewage is collected in a sewage balancing tank (mentioned above) which should be sized to hold at least 6 to 8 hours flow of sewage. This ensures that the sewage collected in the balancing tank is homogenized, thereby avoiding input fluctuations in input load on the STP. Do not compromise on the size of a raw sewage balancing tank.
● High noise levels from an STP are due to the operation of electric motor driven equipment such as pumps, air blowers, air compressors, etc. Old designs/makes of pumps, blowers, compressors, etc. are still available at very low prices in the market and these are used in most of the STPs that have been put up. The noise levels of such equipment is very high as compared to modern, world class pumps and rotary motor driven equipment now available in India. These modern makes are almost noiseless and extremely efficient. The old designs are also the cause of high energy consumption in addition to very high noise levels. As per the laws in force in India, the noise level permitted in a residential area is 55 dB (dB= decibels of sound) during day time, i.e. from 6:00 am to 10:00 pm and 45 dB during night time (10:00pm to 6:00 am).As compared to these limits, the actual noise levels are likely to be as high as 75 dB or higher. To reduce noise levels and high energy consumption, it will be necessary to replace most of the critical rotary motor driven equipment with the latest noiseless high efficiency equipment. Here it is advisable to choose a reputed company with an established reputation in sewage/waste water treatment to buy an STP. Such companies have constantly improved their designs to reduce the foot prints (space occupied) of their equipment and reduction in the power consumption of power by a very appreciable amount. Unfortunately, residents have no say in this as they face up to this crucial fact when it is too late as the STP has been ordered probably even before the residents bought a home in the property.

The prices given here are only indicative and meant to give an idea. All capacities given are in KLD (Kilo litres /day, kilo= 1000 liters).
● 5.0 KLD STP = Rs.5.0 lacs.
● 10 to 15 KLD = Rs.8.0 lacs.
● 25 KLD = Rs.15.0 Lacs.
● 35 KLD = Rs.18.0 Lacs.
● 50 KLD = Rs.35.0 Lacs.
● 75 KLD = Rs.40.0 Lacs.
● 100 KLD = Rs.30.0 Lacs. (All civil work for this size to be built by buyer)
Also please note:
● Prices given are exclusive of Value Added Tax and excise duties (if applicable)
● Supplier will charge a separate amount for installation and starting up the STP. This can cost an additional 5 to 10%
● Prices for MBR systems are not given since they involve a substantial import content and hence it would be better to approach companies that offer such a system for a price directly.

The operating costs, including maintenance for:
● STP of 75KLD capacity and above: 1.2 paise per litre of sewage treated.
● STP of 50KLD and below: 1.5 paise per litre of sewage treated.
These costs do not include the cost of plant operating personnel. If O&M is provided by a reputed company which would use well trained operators with one operator per shift and one supervisor during general shift, they would charge approximately Rs. 60,000. per month. Other obscure agencies who take on O&M contracts would charge approximately Rs. 20,000.00 to 30,000.00 for providing the same number of personnel, but without the necessary training.
Is treatment of sewage rather complicated to understand for an average resident/ owner of an apartment or villa?
Yes, unfortunately, it is true.If sewage treatment was simple and easy for all to understand, this entire write up with FAQs would be much smaller and easy to follow.

Go to the “Ask the Expert” service and you will find that there are several persons with the necessary expertise based in different cities in India. Contact them and ask if they will help and the terms on which they will do so if it involves visiting your location. You will get one of them to definitely offer to help.

Yes, there are a few. Unfortunately, it is too late for Residents’ Associations to do anything about these because they take over a property after it is all over and done. It is the builders who should read this section and hopefully do what is suggested if they have their buyers’ interests at heart.
● Sewage treatment is one of the most crucial features for the residents of an apartment complex/gated community. It needs to be installed in the premises in a location where it is above ground and hence can get all the air it needs for it to function and to facilitate easy maintenance. Never install an STP in a basement.
● Almost all STPs in multi storied apartment complexes are installed as deep underground as possible! From the point of view of an agency that manufactures, installs and probably also operates it, an underground STP is a nightmare! If it stops working, emptying the collected sewage so as to be able to repair it is a terribly unpleasant task. Equally important is the handling of sludge which is generated in appreciable volumes during the normal operation of an STP. This sludge needs to be manually handled as it is coming from the basement. Regular maintenance therefore can become a recurring nightmare for the Operation & Maintenance team.

Something that is extremely important but never done till it becomes too late. A residents’ association must insist on the builder furnishing the association with all documentation of what the property has installed on it, eg, As built drawings with criteria used for designing/selecting, as well as detailed technical specifications for the electrical installations, power generation equipment, complete water infrastructure, piping for fresh water and sewage with drawings showing the routings and this must include the piping for the waste water to and from the STP.
Details of all the pumps and other motor driven rotary equipment as installed with information on how these have been selected, as this will have a crucial bearing on the power consumption in the community. Proper documentation is a must for all the engineering incorporated in a property here, ignorance is not bliss, it is an unmitigated disaster! Without this, maintenance/repairs can become a major problem due to sheer lack of information on all the equipment which is required to undertake planned maintenance.

One option is for the Government (either Central or State) to enact legislation to protect buyers of homes. Another option would be for the various associations of builders to themselves evolve a code of ethics that would ensure protection with regard to providing water security in a totally transparent manner. Neither of these is likely to happen in a hurry ,so, it may be necessary for Residents Associations countrywide to come together and put pressure on the governments and builders to ‘clean up their act’ and do things in a more transparent manner concerning the crucial aspect of water security.

RWH is the technique of collecting, storing and distributing rainwater for multiple uses. The collected water can be stored for direct use or diverted for borewell/groundwater recharge.
In simple terms it is a way to capture the rainwater when it rains, for later use.

You, me and everybody! It will not only provide you with water in times of acute water shortage, but will also recharge the groundwater and increase its level.

Rainwater is the ultimate source of all the fresh water that we use. In India, rainfall occurs in short periods of high intensity, allowing the rain falling on the surface to flow away fast. This leaves little scope for recharging the groundwater, which results in water scarcity in most parts of the country. Through RWH, this erratic rainfall can be conserved, stored & used as per convenience, either directly or for recharging groundwater.

Rainwater is the ultimate source of all the fresh water that we use. In India, rainfall occurs in short periods of high intensity, allowing the rain falling on the surface to flow away fast. This leaves little scope for recharging the groundwater, which results in water scarcity in most parts of the country. Through RWH, this erratic rainfall can be conserved, stored & used as per convenience, either directly or for recharging groundwater.

RWH can be done in homes, apartments, societies, schools, institutions, commercial premises and any other space as long as there is a catchment area in the form of a roof or open space to capture the rain.
Domestic rainwater harvesting is a relatively simpler affair, where even a rain barrel can serve as a storage unit for rooftop RWH. Individual homes have successfully implemented this easy and eco-friendly method of augmenting household-level water availability. Farmers also have implemented RWH to transform a barren piece of land into a self sustainable, lush green farm.

No, existing buildings can also implement RWH by modifying the existing plumbing and making additions, if necessary.

The rainwater harvested depends upon the catchment area, the rainfall pattern in the area and the drainage/ collection system used.
To understand the potential for rainwater harvesting, let's take the example of a house in Delhi with a terrace area of 100 sqm. Taking the average annual rainfall in Delhi as 600 mm, and assuming 70% harvesting efficiency (as some rainwater will be lost due to evaporation, collection etc.), we can calculate the amount of water harvested thus:
Volume of water harvested = 100 x 0.6 x 0.7
= 42,000 litres
This volume is more than twice the annual drinking water requirement of a 5-member family, whose average daily drinking water requirement is 10 lpcd.

The cost will vary depending upon the catchment area and the conveyance/ storage structures finalised. RWH can be installed at a very low cost in large plots where public buildings, schools & colleges are located, and this cost is negligible to the total construction cost, if integrated with the building design.
If planned in an existing building, the cost is higher due to extra plumbing involved, but the returns are rich in terms of recurring benefits.

Various kinds of filters are used in RWH. If the rainwater is to be used for flushing toilets alone, there is no need for any filter but the roof needs to be kept reasonably clean. If necessary, a grating can be fixed at the inlet point to the loft from the roof.
For more: Need horizontal, stainless steel filter for RWH

The rainwater that falls on the roof is pure, but since it comes in contact with various surfaces on its way to the storage units, some dust and leaves may get carried away with it. This can be reduced if the terrace is swept before the rains. However, even if some dust or leaves go into the sump, they do not cause any harm as long as the water is boiled before consumption.
Various filters can be utilised to remove such suspended pollutants from the rainwater collected to make it safer for consumption.

Rainwater harvesting can broadly be divided into 3 categories based on the types of usage, the area in which harvesting is carried out and the people involved.
• Storage or recharge: Based on the type of usage, structures can either be used to store the collected water for direct use or to recharge groundwater.
• Urban-rural difference: Urbanization has resulted in the shrinking of open spaces as well as unpaved areas. This has resulted not only in flooding of cities but has also caused water scarcity due to groundwater depletion in general and saline water intrusion in coastal cities. While rural harvesting is mostly traditional and is carried out in surface storage bodies like rivers, tanks, ponds, lakes etc., urban harvesting, due to lack of open space for capturing the runoff, is mostly in sub-soil storage as groundwater recharge.
• Rooftop & driveway harvesting: When we say rainwater harvesting, the first thing that comes to our mind is the terrace. This greatly restricts the scope of rainwater harvesting as a considerable amount of water that falls around the built-up area is let out of the building as run-off. Driveway run-off water should not be led into a sump for immediate use or to a source well, but it can very well be directed into recharge wells.

• Catchment areas that include roofs of buildings and open spaces.
• Storage units that can be a barrel, a tank or even a sump.
• Conveyance mechanism which transports the water falling on the catchment area to the storage unit.

The RWH system must ensure that not a drop of rainwater falling within the premises is let into the sewerage or wasted as runoff. This can be achieved only if the method adopted within the premises satisfies the following criteria:
• Completeness: Both rooftop and driveway runoff water must be harvested.
• Apportioning of water: To avoid overload of any one system, leading to overflow and loss.
• Proper design: Volume of water likely to flow through and the nature of the soil in the area should be considered.
• Maintainability: Design should incorporate features allowing for periodic maintenance of the structure.

Existing unused structures like dried open wells, sumps etc can be used for RWH as also defunct borewells, instead of constructing recharge structures. This will also reduce the total cost.

It is a process by which the groundwater is augmented at a rate exceeding that obtained under natural conditions of replenishment. Any man made scheme or facility that adds water to an aquifer may be considered to be an artificial recharge system.

Recharge structures are constructed to allow rainwater to replenish groundwater. The various ways in which recharge can be done is through:
• Abandoned dugwell
• Handpump
• Recharge pit
• Recharge trench
• Gravity head recharge tubewell
• Recharge shaft

A recharge pit is a hole dug in the ground, usually filled with gravel or jelly to give it structural strength. However, a recharge well is not filled with gravel, but needs concrete rings installed in it to stabilise its walls.

For effective recharge in Bangalore like conditions, a 15-20 feet depth is needed. (Provided you do not hit rock before that depth). If you hit water while digging the pit, you need to ask the workers to be careful while they continue digging. The diameter of the pit you choose depends on two things: space available and the quantity of water you will send in. A 3 feet dia X 20 feet pit will ‘hold’ around 4000 litres (for recharging the ground). A 5 feet x 30 feet structure can hold 16000 litres.

As per the law, you need to store or recharge 20 litres for every sq.m of roof area and 10 litres for every sq.m of non-roof (ground surfaces such as parking, backyard) area. This is for plot sizes of 40x60 sq.m or more. For e.g. if your home has about 100 sq.m of roof area, and about 50 sq.m of non-roof area, then you will need to create capacity for at least 2500 litres of water. If you are using a 1000 litre tank to store rainwater for immediate use, you can connect the overflow to a 4000 litre (3 feet x 20 feet) recharge well.

The cost of digging a 3 feet diameter well, which is 20 feet deep, is approximately Rs 20,000.

3 steps to begin RWH:
Step 1: Ask yourself: Why Rainwater Harvesting? Your answers to the questions below will help determine the most appropriate RWH interventions. In many cases RWH is implemented to achieve all three of these objectives.
o Is it a source of supplemental water (thus reducing demand from your existing sources)
o Is it to recharge ground water sources as you are dependent on borewells/open wells?
o Is it also a flood control measure?
Step 2: Understand the strategy for your layout.
o Consider the land use pattern
o Choose domestic RWH system with storage tank or use an existing sump as storage
o Need for investing in recharge wells
o Engagement with people, discussion with other residents as water managers
Step 3: Talk to an expert How to deal with the technicalities of direct storage and groundwater recharge? For answers to common yet crucial questions related to RWH that address the technicalities of direct storage and groundwater recharge, you may refer to this Technical FAQ.

The benefits include:
• Flood mitigation: Appropriately designed recharge structures in open public spaces, will help keep the roads from flooding. When water is not allowed to leave the premises, the chances of it choking up the roads are minimal.
• Increasing groundwater levels: Marked improvement of both the quantity as well as the quality of the groundwater in areas which have implemented rainwater harvesting
• Greater water availability: Rainwater collected in storage tanks is available as and when needed
• Prevents soil erosion and flooding especially in urban areas

RWH can be traced back to thousands of years in India. Our ancestors traditionally harvested rainwater through tankas, johads, madakas and many such local innovative structures that can be seen even today, across the country.

The Reverse Osmosis FAQ, is meant to provide a section dealing with TDS in RO Systems, clear what the term means and how relevant an RO system is to the readers.

As per the Bureau of Indian Standards, the desirable quality of drinking water is that which has TDS (Total Dissolved Salts) content of 500 ppm or less (ppm stands for parts of the salt present in a million parts of water, 1 ppm = approximately 1 mg/L ). Where water of this quality is not easily available, the compromise/permissible level is water having upto 2000 ppm. It is to be borne in mind that in some places, iron salts may be present and if the content of iron salts is more than 0. 3 ppm, even if the total salt content is less than the desired level, the iron salts will have to be removed before drinking that water. There are also some pockets West Bengal and U.P. where the water contains Arsenic. This is poisonous and so here also the same rule applies. In some pockets again, fluoride salts may be present which affect the bones if that water is drunk. Using this water for non-potable purposes is however not harmful.
Another point to be remembered is that water with very low salt content is not very palatable and therefore where the total salt content is less than 500, reducing it to 10 or 20 by RO is not only meaningless from the point of view of wastage of water but also from the cost and loss of palatability aspects. In cases where the salt content is not much higher than 2000 ppm, a simpler route would be to harvest rainwater which will dilute the salts and bring it within potable limits progressively.

RO is a process where water having more than the desirable salt content is put in one part of a vessel with two compartments separated by special media and pressure is applied on the water. This results in only the pure water going across the media to the other compartment with the salts remaining in the same compartment. Thus the process results in accumulation of salts in the first compartment. Beyond a certain concentration of salt the process will not proceed further and the water which contains all the salt is rejected.
Because of this, if one starts with say 100 parts of water, the process yields only about 70 parts of good water and the other 30 parts which contain all the salts present originally in 100 parts have to be thrown away.

In RO systems of small capacity suitable for domestic purposes, the rejected component may be as high as 45%. The process therefore is a wasteful one with much of the water having to be thrown away. Diverting large volumes of this highly salty water into the sewage line could result in acting against the smooth movement of its contents. The reject will not be tolerated by normal garden plants. It will form deposits on the floor and sanitary ware. It is also not advisable to divert it to the septic tank. If the water subjected to RO has less than 1000 ppm say, then the salt content in the reject water will not be much and it can be used for gardening or flushing. But the point is that this water need not be subjected to RO at all in the first place.

· RO is to be resorted to only in cases where the salt content of water to be used for drinking is much higher than advisable.
· Even here reduction of the salt content to the level of 10 or 20 ppm is counterproductive. If the salt content of the water is very high even for non-potable purposes, rainwater harvesting often works wonders.
· In the cases where the water contains coliform bacteria, the source for their presence should be traced and the contamination eliminated. While RO may be advised, elimination of the cause is the safer and preferred route and ultimately the cheaper route also.
· Those who go in for RO for water with high salt content are well advised to assess the volume likely to be subjected per day and ask the supplier how long will the media work effectively with that volume, what is the cost involved for the replacement of the media and what are the monthly running costs, apart from the capital cost.
· They also should question any proposal to reduce salt content to less than 500 ppm.

· The most popular FAQs are listed below. Please click on a topic to view more detailed information:
· What do you mean by TDS ?
· What are the standards for TDS ?
· How to measure TDS content ?
· What are the methods for TDS mitigation ?

TDS is Total Dissolved Solids. Water dissolves the minerals present in the strata of soil it filters through in the case of ground water and, in the case of surface water, the minerals present in the soil over which it flows (rivers/streams) or over which it stands (lakes, ponds, reservoirs).The dissolved minerals in water are commonly referred to as Total Dissolved Solids (TDS). The TDS content of any water is expressed in milligrams /litre (mg/l) or in parts per million (ppm). These units are equivalent.
The minerals are basically compounds (salts) of Calcium(Ca), Magnesium(Mg) and Sodium(Na) What is commonly called as ‘hardness in water’ is due to the compounds/salts of Ca and Mg such as Calcium or Magnesium Chloride, Calcium or Magnesium Sulphate ( CaSo4, MgCl, etc).Some types of dissolved solids are specifically dangerous even in low quantities. This includes arsenic, fluorides and nitrates. There are particular standards for the acceptable amounts of these elements in water and in some cases like fluoride, there is some disagreement as to what constitutes safe levels.
Leaving aside the specific harmful chemicals fluoride and arsenic, drinking water for human beings should contain some level of minerals (TDS), but these levels should not be excessive.

India Standards: The standard that applies to India is the BIS 10500- 2012 standard This standard used the WHO standard as the basis and has been amended subsequently to take into account the fact that over exploitation of ground water which has the largest share of water supplied for human use has deteriorated to such an extent that the crucial parameters such as TDS, hardness, Chlorides, etc usually exceed the desirable levels substantially. Consequently, a higher permissible limit has been specified. Water used for drinking becomes unpalatable when the TDS level is above 500 mg/l, but lack of any better source enables people consuming such water to get used to its taste. The BIS standard applies to the purity level acceptable for human beings to drink. For practically all industrial and some commercial uses, the purity levels required are very much higher and in most cases demand water with virtually no residual dissolved solids at all. BIS Standard says that the maximum desirable TDS is 500 mg/L and the maximum permissible level in the absence of a better source of water is 2000 mg/L. A related standard is the 'hardness measured as CaCO3" where the acceptable limit is 200 mg/L and maximum permissible is 600 mg/L.
WHO Standards:
"Water containing TDS concentrations below 1000 mg/litre is usually acceptable to consumers, although acceptability may vary according to circumstances. However, the presence of high levels of TDS in water may be objectionable to consumers owing to the resulting taste and to excessive scaling in water pipes, heaters, boilers, and household appliances (see also the section on Hardness). Water with extremely low concentrations of TDS may also be unacceptable to consumers because of its flat, insipid taste; it is also often corrosive to water-supply systems "
Reference: https://www.who.int/water_sanitation_health/dwq/chemicals/tds.pdf
US EPA Standard:
The U.S. Environmental Protection Agency (EPA) recognises broadly two categories of drinking water standards, known as maximum-contaminant-level goal (MCLG) and secondary maximum contaminant level (SMCL). The MCLG is a health goal set at a concentration at which no adverse health effects are expected to occur and the margins of safety are judged “adequate,” while the SMCL is a non-enforceable guideline that presents no risk to human health. While fixing no limit for MCLG, the EPA has fixed an upper limit of 500 mg/L for SMCL. This limit has been fixed to avoid undesirable aesthetic effects of odour, taste and colour that could be felt by consumers and technical effects of corrosion, incrustation, staining, scaling and sedimentation of pipelines and other fixtures that convey water. Despite not fixing a limit to MCLG of TDS, high TDS water can have certain other constituents at harmful levels of SMCL to cause adverse health effects. Thus MCLG can be a few times more than the SMCL.
Very low TDS:
Due to insipid or bitter taste and lack of useful minerals, too-low TDS also causes problems. There does not seem to be a generally accepted lower limit, but 80 mg/L may be used.

TDS can be measured very fast using a low-cost portable conductivity meter (TDS meter) calibrated to give TDS directly by anybody with extreme ease. It costs hardly Rs. 2000/- and the only recurring expenditure is occasional replacement of batteries. It is worthwhile for users of well water, piped water and packaged water and practitioners of rainwater harvesting and groundwater recharging to test water TDS as a matter of routine. It may be noted that TDS of rainwater is only a few tens of mg/L. Any sudden increase in TDS of water is a signal that water is getting contaminated with some high-TDS water.

UV, UF and other conventional filtration methods will not affect TDS. The only one which works is Reverse Osmosis
Reverse Osmosis:
RO is the only commonly used domestic filtration system that removes even the dissolved impurities. RO is required if the Total Dissolved Solids (TDS) exceeds a certain value. (what is the upper limit ? Look for discussion on that elsewhere in IWP). RO is also suggested if you have reasons to believe that your water may be contaminated with sewage/ pesticides/ heavy metals/ industrial effluents.
A problem with RO is, it needs a lot of water. It divides the input water in two parts, and forces the dissolved solids out from one part in to other. Thus, the output comprises two streams of water – a “clean” stream with low TDS and cleaned of other impurities too. And a “reject” stream that is even more dirty than the input water. Typically, an input of 3 liters will give 1 liter of clean water and 2 liters of “reject”. Theoretically, the “reject” water can be used for mopping the floor etc. but few have the discipline to do that.
Reduction of TDS changes the taste and pH of water, and it is not good to reduce the TDS too low. Some manufacturers make a hybrid machine that combines RO with either UV or UF. Bulk of the water is processed by RO, to remove dissolved solids; and some is processed by either UF or UV, to kill micro-organisms, but retaining the dissolved solids. The two are combined to restore the dissolved solids to some lower limit. The ratio of mixing the two can be controlled by user. The cost of RO systems is in the region of Rs. 10,000/- to 15,000/- The RO works under some pressure, which is developed by an internal pump, and therefore it needs electricity to operate.
With very high TDS levels in the 1000s, conventional domestic RO units may not be able to work effectively. Rainwater harvesting is a useful permanent solution where other sources of water have unacceptably high levels of TDS or hardness. TDS of rainwater is a few tens of mg/L Water softening does not reduce TDS. In water softening sodium replaces calcium and magnesium, in the dissolved solids which causes a minor reduction only in TDS.

Natural mineral water is water from underground sources that is packaged close to the source and meets the specified quality standards without any processing.

Packaged drinking water uses water from any source which has to be treated and disinfected, a process that could involve filtration, UV or ozone treatment or reverse osmosis (RO) before it is fit for human consumption.

There are mainly 4 sections in a packaged drinking water plant: water treatment, bottling, quality control (lab) and overall utility. Generally, a standard 2000 LPH packaged drinking water plant needs: · Total space: 5000 Sq. Ft built up area with 3000 Sq. Ft of covered area
· Power: 65 HP
· Raw water: Approximately 3000 LPH of raw water of which 70 % will be used and 30 % will be rejected. This is, however, an indicative quantity as it will depend on the TDS (Total Dissolved Solids) of the raw water.
· Project cost: Rs. 75 lakh approximately which includes the cost of machinery, utilities, furniture etc (Note – the cost was approximated in 2013).

According to market sources, a litre of packaged drinking water is Rs. 10-12 while natural mineral water starts at about Rs 20 a litre and can go up to Rs 125.

According to the International Bottled Water Association, it takes on average an estimated 1.39 litres of water to produce a litre of bottled water.

The following licenses/ approvals are to be obtained for setting up a packaged drinking water plant in India: · Small scale industries registration
· ISI certification from Bureau of Indian Standards (BIS)
· Pollution control certificate
· Water test report from an authorized laboratory of raw water
· Pest control certification
· Certificates from chemist, microbiologist
· Medical certificates for workers
· No objection certificate (NOC) from Gram Panchayat, if applicable
· Registration of trademark
· Documents related to ownership of land/lease of land for setting up the plant
· Memorandum of association of companies/partnership deed, if applicable.
· Electrical load sanction
· Sanction layout plan

Yes, it is compulsory for all the manufacturers who intend to set up processing units, to obtain the ISI mark from the Bureau of India Standards. Packaged Natural Mineral Water is governed under IS:13428 and Packaged Drinking Water governed under IS:14543. For more details please refer https://www.indiawaterportal.org/FAQ-rules-regulations-standards-concerning-water#ISpackagedwater

No. Unless the official inspection of the plant, tests in an independent lab are carried out and official approval with license number is obtained, the unit cannot commence commercial production.

Yes, such a lab should be equipped to carry out all physical, chemical and micro biological tests prescribed as per IS:3025, and has to be conducted by expert chemists /micro biologists.

Yes. As per a notification issued by the Ministry of Consumer Affairs on Feb28, 2001, amending Standards of Weights and Measures [Packaged Commodities] Rules 1977, it is mandatory now for bottled water to be sold only in prescribed standards. These are 100 ml / 150 ml / 200 ml / 250 ml / 300 ml / 330ml [ only in cans ], 500ml / 750 ml / 1 liter / 1.5 liter / 2, 3, 4, 5 liters and thereafter in multiples of 5 liters.
Is it permissible to run a soft drink unit and bottled water unit from the same premises? No. Since the ingredients to be utilized in soft drink [sugar and flavor] are likely to contaminate the surroundings and equipment, it is neither advisable nor permissible to operate the same units out of one place.

The plastic material used to contain naturally sourced bottled waters found on supermarket shelves is made of PET (Polyethylene Terephthalate) and is completely safe.

Single-use plastic water bottles are not designed for reuse. In the interest of hygiene and consumer safety, it is not advisable to reuse single-use bottles for storing water. However, they can be reused for other purposes like planters, drip irrigation etc.

Naturally sourced bottled waters have different concentrations of minerals in them, depending on the geology of the land that they come from, which gives each bottled water a unique taste.