920 million litres of water wasted daily in India through RO filters

Do we really require Sabse ‘Shuddh’ Paani?

For every one litre of purified water, three litres of water is getting wasted through Reverse Osmosis

Back story :

Mr. A is a healthcare practitioner. One day, his neighbor, Shiela aunty, came to him to flaunt her newly installed RO filter. She believed it was crucial to consume highly purified water in order to stay healthy.

When Mr. A asked her what was the TDS before and after the installation. She replied “TDS kya hai beta”

TDS stands for Total Dissolved Solids and is measured in PPM (particles per million). However, TDS alone does not represent the amount of impurities present in the water; important minerals like calcium and magnesium are also reflected in the PPM (particles per million).

The Problem :

The problem is that RO is not necessary for TDS < 500 ppm. If your source water TDS is less than 500 ppm, you do not need a filter with RO. Normal sediment filtration, carbon filtration, and UV/UF alone might be sufficient without RO. However, sales-focused companies use “RO” as their marketing buzzword to sell their products.

Consumers are unaware, so companies keep the TDS very low, stripping all minerals from the water. TDS is deliberately kept low to make the water taste sweeter.

I can’t emphasize enough how important minerals (electrolytes) are, as many chronic diseases can be cured simply by keeping the main electrolytes at an optimal level. Other than sodium, most of the Indians are chronically deficient in Mg, Ca & K.

A few years ago, the green tribunal gave directives to ban RO purifiers for <500 ppm (this was stayed by the Supreme Court due to policy issues). Companies cleverly introduced a TDS controller, but this controller doesn’t completely bypass the RO membrane. It is like a valve; you can only adjust the flow of water. So, even if it is released completely, water still partially flows through the RO membrane, discharging 3.25 times the input water.

       WHO's recommended  limits 

             Calculation Data

The solution :

For the sake of comparison, Saving all the discarded RO water for three consecutive days by us Indians would be adequate to fulfill entire Africa’s daily requirement for drinking water.

We need to either remove the RO membrane where TDS is less than 300-500 or efficiently reuse the discharged water by using reject water tanks.

I will discuss a detailed solution soon. If planned correctly, this will be much more convenient for new constructions or high-rise buildings.

Part 2 of this write-up will be available in the future.


@Mr_A I have a question. I am scared to have water from the pipes without it going through a filter. If not RO, what else? Are you saying we can take the risk of drinking tap water without any filtration?

@Mr_A we should also include other parameters for the shuddh paani, when we have around 80 percent population consuming ground water. It is vulnerable to heavy metal such as arsenic, cadmium lead etc. And this surely cannot be ignored when around 209 districts have arsenic above acceptable limits in the ground water.

Heavy metal poisoning has been a major cause of skin disease and neurological disorders.
Eager to know, if the alternative you propose accounts for heavy metals.


RO is just one part of the entire filtration process. ‘RO membrane’ is optional if your TDS is in the nominal range.

Even if someone considers using RO, some arrangements need to be done to reuse the discharged water for washing utensils, cleaning the garage or gardening, etc. (of course it depends on the hardness of the discharged water as well)

At least, a collection beaker needs to be there through which one can reuse the water

However, the entire process can be automated if you can discharge the water to the rainwater system or your overhead/underground water tanks. (It’s easier for the under-construction buildings, as the plumbing can be planned priorly)

Much awareness about this is needed. Wastage of BILLION litres of water every single day is unacceptable.


How much water gets wasted, say, for every 1 litre of post-filtered RO water?

As I have mentioned in the post, other filtration elements like sediment filter + Carbon filters + UV/ UF needs to be certainly used. Carbon filter eliminates metals from the water.

Arsenic & other elements are present in most of the grains Indians consume, including brown rice & wheat. What could we do? Even RO can’t completely remove the Arsenic from the drinking water.

The ground water consumption percentage you have mentioned is relevant to the rural population but the urban population is predominantly dependent on municipal water (piped water)

Anyway, Let everyone have their individual preference to use the RO function or not. It would be great if we could give any solutions for re-utilizing the discharged Water.

I have a few & I will share those in the subsequent write-ups. We need not rely heavily on the ground water in the future.

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For every 1 liter of filtered water, a RO purifier discharges (wastes) around 3 liters of water

Activated carbon filters look very promising.
Also CMERI, a public research institute has developed high flow iron and flouride filtration technology based on adsorption and gravity settling. This technology is said to be viable for community water filtration systems which can reduce the need of RO system altogether if installed in housing societies and urban townships.

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Damn, I didn’t realize. I need to go figure out where that water in our house goes to.


So in our house all the waste water gets collected in a separate tank, post filtration it gets used for gardening and cleaning common areas.


Here’s a quick how-to from our partners Biome




BTW, if the TDS isn’t too high, you can use a non RO (UV) filter - those do the job. Of course with each round of service and change of candles etc the plastic waste is still a headache and the companies do NOT collect it.


Along with the TDS check we can also go through comprehensive water quality tests. So that we dont end up using filtration systems some salesman has sold us rather we are using what we actually need.

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Lot of us in Bangalore use Cauvery water. Is the TDS same for anyone using this water across the state or does it vary?

We use a carbon water filter at home (central bangalore). RO is a good mechanism in high-salt areas (Rajasthan, Kutch etc) or where drinking water is sourced from Coastal waters (Israel). Else, in my opinion it is quite a useless solution. At least 3litres of water is wasted for 1litre of ‘filtered’ water; filtered out of important minerals and essential salts.
RO filters have been a personal peeve for long, and I wrote about this sometime ago. Unfortunately, there’s little to no compliance of the NGT order to ban ROs where tds is below 500… but then lobby groups… and in the meantime RO sales/growth is business-as-usual with periodic mainstream narrative being reinforced…

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Yes, TDS will vary in different areas. Many reasons (filtration plant capacity/health/age, age and maintenance of water pipes, possible contamination during supply, etc).
BWSSB does (I believe, fortnightly) tests and you can download these reports for your area from this dashboard to check the TDS/water quality in general… been a hit-and-miss whenever I’ve tried to use this dashboard though.

@Mr_A What about the good old steel filter cans that come with filter candles? I remember growing up on these but got lost with these ROs for a few years … now back on these filter candles, it’s been 6 years that we are drinking water out of these again. In-between, for a couple of years, we also used these to filter water coming straight out of a mountain forest stream. We haven’t fallen sick and the water tastes super sweet! :slight_smile:

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WATSAN is an interesting solution as a replacement for ROs. These guys have been doing great work for the past few years.

Successfully seen their larger filters being tried out in places with 100-150 people drinking water from them everyday.



It says everything. So, you might not worry about any additional filtration & continue with the same. Natural water tastes sweet as the minerals are retained and the pH is being maintained.

We envy you

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Firstly, an RO filter is not always necessary.

Understanding the quality of available water before opting for an RO filter is important. An RO filter is necessary only when the water supply has chemical contaminants like Total Dissolved Solids (comprises of inorganic salts & small amounts of organic matter). Or if your tanker/borewell supplies hard water. Cauvery/rainwater does not need to go through an RO filter. A simple sand filter will suffice in this case.

But when you do need an RO filter, here’s why you should reuse the wastewater from it:

RO systems reject 30-50% of freshwater while purifying. They reject 5-8 litres of water for every litre of fresh water. All this water usually goes down the drain. Instead, we can reuse it for various purposes like washing clothes, dishes, watering our garden, mopping, etc.

How do you do this?

An easy and straightforward way is to set up a drum or a bucket below the filter, collect the water and put it into a washing machine, use it to swab floors, etc. But there is another creative way through which you can more efficiently reuse wastewater for your chores.

The filter has a small pump in it that pumps out the rejected water. This means that the water can rise. Essentially, you can allow for the rejected water to be stored in a tank above the RO filter as well, and not necessarily only in a drum below. This makes the subsequent use easier as the water flows down with gravity.

Here’s a creative from Biome’s post about the same: Biome Environmental Trust on Instagram: "Since most of us install an RO filter in our kitchen, what better place to reuse the wastewater than at the sink? RO waste water contains a high amount of salt- a great preventer of stains. Salt will help food particles from sticking to your utensils and also ensure clean dishes. Do keep in mind that the wastewater from RO filters is generally high in TDS, and this can affect soil fertility over time. So it’s best to dilute the RO reject water with some tap water before using it to water your plants. #reverseosmosis#sustainablehomes #reverseosmosiswater #reverseosmosissystem #reverseosmosissystems #reverseosmosisfilter #ROfilter #wastewater #reuse #watermanagement #sustainabilitytips #sustainableliving"

Use a TDS meter to measure the RO reject water and then take a call on the end use. While a TDS of 500 ppm is desirable for drinking water, up to 2000 ppm is also ok for drinking, in the worst-case scenario and in the absence of other sources.

Here are two other useful video links on RO myths busted: