There’s a high chance that your civic body-supplied water does not benefit by undergoing reverse osmosis (RO) process, unless you live in a desert, in an industrial zone, a pesticide-polluted region, or source water from the sea.

RO technology is not applicable to all water types. Even the Indian water purifier industry admits this. “RO cannot be universally applicable for all water types due to key technology limitations. Since RO works on very tiny pore-sized membranes molecularly separating out dissolved chemical contaminants, it cannot, by design, discriminate between so-called ‘good’ and ‘bad’ chemicals,” states the Water Quality Association India (WQIA; among the association’s ‘gold members’ are market leaders Aquaguard, Kent, Eureka Forbes and Ion Exchange of Zero B among others).

What the association is saying is that reverse osmosis eliminates all chemical contaminants (ions, metals, pesticides, particles, etc.) in the water. This means an RO purifier will remove all minerals from the water irrespective of whether these are good (such as iron, calcium, potassium) or bad (fluoride, arsenic, chromium) for your health. But manufacturers of RO water purifiers tend to dismiss this by saying that water is not the primary source of minerals for your body, implying that it’s perfectly alright if your water is devoid of them. This is just part of the problem.

The process of reverse osmosis eliminates only chemical contaminants from the water. The RO process gives a free pass to all biological contaminants i.e. bacteria and viruses in the water. WQIA, the Indian water purifiers’ trade body, testifies when it states, “Biological contaminants can be removed using various technologies like UV, Ozonation, Ultrafiltration, Biocidal resins and allied materials.” Some RO water purifier manufacturers get past this by making premium models that combine RO and UV. But there’s some evidence that these don’t work either. “Despite tall claims, most water purifiers sold across India do not completely eliminate viruses like Hepa­titis E,” was the National Institute of Virology’s assessment of eight water purifier brands in 2015.

It’s all about the TDS

RO water purifier salesmanship boils down to one factor – total dissolved solids or TDS in short. TDS are dissolved salts and compounds in the water that cannot be removed by simple filtration. And indeed RO water purifiers are effective on this count, especially in places where pesticide use contaminates groundwater (states such as Punjab), in desert regions where the salt content is high, in industrial areas where effluents are discharged without proper treatment, or where seawater is the main source of supply. The problem starts when RO purifiers are pitched as household solutions for optimal TDS in places other than the above-mentioned areas.

To put this in context, TDS are classified as secondary contaminants in water. It affects the cosmetic properties of water i.e. if there is a high amount of total dissolved solids in the water, then the water will appear murky. Water appears clear when it has a lower concentration of TDS. According to the World Health Organisation (WHO): “Total dissolved solids (TDS) is the term used to describe the inorganic salts and small amounts of organic matter present in solution in water. The presence of dissolved solids in water may affect its taste.” That’s right, taste and palatability. Not purity.

Water with TDS less than 300 mg/litre was deemed excellent by WHO’s panel of water tasters in a report prepared as reference material to set new water guidelines in 2003. Water with TDS between 300 and 600 mg/litre was good; water with TDS between 600 and 900 mg/litre was fair and water with TDS between 900 and 1200 mg/litre was poor. Water with TDS over 1200 mg/litre was unacceptable. On the other end of the spectrum, “water with low concentrations of TDS may also be unacceptable because of its flat, insipid taste”.

In its drinking water specification, the Bureau of Indian Standards (BIS) prescribes TDS of 500 mg/litre as acceptable. This – TDS <500 mg/litre – is a widely accepted benchmark for water quality and taste. In the absence of alternative sources of water though, BIS specification says TDS up to 2000 mg/litre is the permissible limit.

Bengaluru’s case

In Bengaluru’s case, a recent water quality test (Nov 30, 2019) by the Bangalore Water Supply and Sanitation Board (BWSSB) showed TDS at 206 mg/litre before the water was treated, and 207 mg/litre after the water was treated (IIIrd stage) for potability. This means that TDS for raw water was well within the prescribed range even before treatment, and in fact, increased marginally after treatment.

It’s wise to disregard the civic body’s own laboratory report for its own water quality in the interest of skepticism. But other studies in the past too indicate that except in some areas, Bengaluru’s water (ground water and from the Cauvery) is within the TDS <500 mg/litre standard. A 2015 study that tested the city’s water for pH (acidic-alkaline value) and TDS found that 82.66 per cent of the total samples were found to be below the permissible TDS range. For TDS, “Central region of Bangalore demonstrated 100% potability, east and west regions showed >90% of the same, whereas south-east was poorest of all with 63.88%. Two areas in south-east, in particular, showed an alarming level of TDS of > 1000ppm consistently raising the question of water quality from the total dissolved solid point of view,” the study observed.

Another study, by Karnataka’s Department of Mines and Geology, examined Bengaluru’s borewell water i.e. groundwater quality from January 2009 to January 2010 and found that “68% of samples had TDS ranging from 500mg/L to 2000 mg/L. While this range is permissible by Indian drinking water standards, the water filtration companies have been scaring people about TDS being higher than the desirable level of 500 mg/L. Hence the proliferation of RO systems in the city of late. Water with high TDS indeed might have an undesirable taste and may not be comfortable to bathe in, but the scare raised by sales people should be taken with a pinch of salt”.

A ban in the pipeline

RO water purifier marketing stands on pillars of doubt and spreading fear of TDS. Sure, RO water purifiers can be an answer to potable water in places where TDS levels are on the higher side, including in Bengaluru’s polluted and industrial areas. But this does not give RO water purifier manufacturers latitude to peddle their wares in places where these apparatuses wreak environmental havoc (more on this later).

And yet they brazenly do so; the Indian residential water purifier market (RO and non-RO purifiers) has witnessed double-digit growth in the last decade. It is currently valued at $391.4 million and is expected to grow at an annual rate of 13.3% to reach $818 million by 2024, according to Research and Markets agency.

India does not regulate the water purifier industry is a contributing factor to the industry’s success. But it doesn’t bode well for a nation – especially where thousands suffer from/die due to water-borne diseases each year – when private companies make parallel inroads into a critical civic function on the basis of misinformation. This is partly why, the National Green Tribunal (NGT), a statutory body set up to expeditiously deal with all environment-related issues, stepped in. This May, the tribunal ordered the Ministry of Environment, Forest and Climate Change to issue a notification banning RO water purifiers in places where TDS are below 500 mg/litre. Last month, the Tribunal’s chairperson Justice Adarsh Kumar Goel told the environment ministry that if the RO water purifier ban notification is not in place by the end of the year (31 December 2019), then the concerned ministry officials’ salaries will be withheld from January 2020.

A criminal waste

It is pertinent at this stage to take stock: RO water purifiers eliminate chemical contaminants, including healthy minerals, from water. These chemical contaminants, measured as TDS, need to be gotten rid of only if present in higher concentration i.e. >500-600mg/litre. RO water purifiers do not take care of biological impurities. The technology is good only for certain “water types”. And yet RO water purifiers are as ubiquitous in towns and cities in north India as they are in the South and the West. Their manufacturers, one can argue, are healthy companies that no doubt generate much employment and revenue. Why then is the NGT so determined to ban them in unrequired areas?

It’s because RO water purifiers push out significantly more ‘reject’ water than they purify. For every one litre of potable water, RO water filters push out three to four litres water, as per broad estimates. Some manufacturers claim that their brands result in minimal reject water and up to 60 per cent purified water. According to the Water Quality India Association, RO achieves 20-30 per cent purified water and 70-80 per cent is drained; this ‘reject’ water is saline as it has a higher concentration of chemical contaminants.

The ‘reject’ is a colossal waste of a precious resource although the industry claims otherwise: That the reject water can be used to wash utensils or to swab floors and even to water plants. We’d be wiser to take this claim about saline water with more than a pinch of salt. At least one study on the use of RO reject water for plants demonstrated that it inhibited the plant’s growth.

And if you think you can flush the toilet, swab floors or wash your car with this water, think again. Saline water leads to corrosion in metals. This reject water will eventually find its way into the ground, contaminating everything along the way: Sanitary ware, fixtures, pipes and drains will corrode over time, and guess what it’ll do to the ground water…. more TDS! Prolonged RO water purifier usage will mean we are only adding more and more chemical contaminants to the ground water which we will again put through RO water purifiers, and the cycle continues. In the long term, this will not only impact ground water quality, but also soil and agriculture.

The only responsible way for ‘reject’ water from RO water purifiers is to treat it before discharging it in any manner. This falls in the realm of scientific and industrial operations (recovery of minerals, salts, etc.) and is certainly out of the purview of domestic and household chores.

Add to this the fact that RO works only when there is a continuous supply of water at a consistent, predetermined pressure. This means you can never turn off the water supply to your kitchen RO. Ergo, there’s a constant outflow of reject water from RO water purifiers. If you have a household RO water purifier and live in a town where it isn’t required, you are wasting water 24 hours of the day, 12 months of the year, every year. How is this a solution?

(Marisha Karwa is an independent writer)

The views expressed above are the author's own. They do not necessarily reflect the views of DH.