What is the debate around RO water?- THE HINDU- 09/02/2020 - PRELIMS

What is the quality of water globally?

Countries with a high development index tend to have good quality tap water.

Finland, Denmark, Switzerland, Germany, United Kingdom have access to freshwater lakes or glacier melt — extremely clean and mineral rich. This water is further filtered.

Singapore and Israel rely on extensive recycling and even making sewage water fit for drinking.
The limited population pressure, compared to India, as well as public resources allow these countries to ensure clean drinking water.

But for much of the world, access to clean piped water from the public supply remains a challenge.


The Central government has drawn up plans to ban the use of Membrane-based Water Purification Systems (MWPS) – primarily Reverse Osmosis (RO) systems in areas where the water supplied meets the Bureau of Indian Standards norms.


The National Green Tribunal (NGT) prohibited the use of RO purifiers in areas where Total Dissolved Solids (TDS) levels are below 500 mg per litre.

NGT sought a ban on RO filters because they waste water and in the process of removing salts, “they often deprived drinking water of essential salts”.

Home filters waste nearly 80% of the water during treatment.

Some research has shown that the process can cut the levels of calcium and magnesium, which are vital nutrients.

RO process

Reverse Osmosis (RO) is a water treatment process that removes contaminants from water.
It uses pressure to force water through a membrane that retains the contaminants on one side and allows the pure water to pass to the other side.

RO purification units involve two processes. The unit consists of two filters:
1. A carbon or sediment filter, also called Pre-Filter and
2 . A semi-permeable membrane.

The Pre-Filter removes large particles from the water before it passes through the semi-permeable membrane.

The Membrane allows water to pass through but traps pollutants and bacteria in its porous surface.

In RO, the TDS in water — which covers trace chemicals, certain viruses, bacteria and salts — can be reduced, to meet potable water standards.

Issues with the system: The storage tank must be cleaned periodically.
Damaged membranes are not easily detected, so it is hard to tell if the system is functioning normally and safely.

Purpose of the draft

The government’s draft notification prohibits RO purifiers in areas where water quality meets BIS standards.

The aim is to ensure that after 2022, no more than 25% of water being treated is wasted.
For residential complexes to reuse the residual waste water for other activities, including gardening.

Once the rules are finalized, RO machine manufacturers will have to tweak their designs to meet the new parameters so that the system does not discharge water beyond the prescribed limit during the purification process.

As far as monitoring and enforcement are concerned, the draft left it for BIS to develop a system to monitor, assess and certify in consultation with the Central Pollution Control Board (CPCB) within six months of final notification.

Enforcement will largely be the responsibility of CPCB and State Pollution Control Boards (SPCBs).
The notification thus implies these filters are only prohibited if the home gets water supply that conforms to the Bureau of Indian Standards (BIS) for drinking water.


Although several State and city water boards claim BIS standards, the water at homes falls short of the test parameters.

The BIS in 2019, ranked several cities on official water supply quality.

Delhi was last on the list and only Mumbai met all the standards.

In the 28 test parameters, Delhi failed 19, Chennai 9, and Kolkata 10. The BIS norms are voluntary for public agencies that supply piped water but are mandatory for bottled water producers.

Moreover, most of the country does not have the luxury of piped water.

The Composite Water Management Index (CWMI) of NITI Aayog says that 70% of water supply is contaminated. India is ranked 120th among 122 countries in an NGO, WaterAid’s quality index.
The case for restricting people’s choices on the means they employ to ensure potable water is thus weak.


The government can come up with changes in the method of water purification but it must delay the crackdown on ROs in so-called “safe supply” areas until consistent evidence through regular and well-publicized water quality tests can convince the skeptical public.

Therefore, the need is to first reassure public about water quality, then regulate the use of RO purifiers.

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