RO water purifiers waste large quantities of water, silver nanotechnology can be harmful in the long run…

Water has been a common theme in this column the past few weeks. The emphasis has been on reminding ourselves that we cannot take water supply for granted and there is an urgent need to consume safe products that will save water in our homes.

In this context I would like to record my recent experience with buying a new water purifier. It started off as a simple purchase of the latest technology in purifiers but took several surprising turns and threw up valuable insights which should be useful to everyone. My last water purifier used UV technology to purify water. UV rays are used to stun the bacteria in the water and render them inactive so that they can safely pass through our system without causing diseases. However this also means that water purified by UV rays cannot be stored for more than a few hours as the attenuated bacteria could get reactivated.

I had last purchased a purifier five years ago when the concept of RO (Reverse Osmosis) was nascent, unlike today where RO filters are the norm. So imagine my consternation when I was casually told by the store salesman that an RO filter would waste 60 to 70 per cent of water. I cannot think of any way to justify this wastage, certainly not in water-starved Chennai. I followed this point with a few friends who were using RO filters and I received confirmation that for each litre of potable water delivered by the RO unit, almost four litres of waste water was generated. The RO system was originally invented to create potable water from otherwise unusable sea water and was never meant for filtering ground water. Then why are lakhs of Indians buying RO systems? The main reason is the fear of water-borne diseases. However I have not come across any study that conclusively proves that RO systems are more effective in preventing them.

My old UV filter broke down because the internal circuits were shot and that particular model had been discontinued. Therefore the option of a manual or mechanical filter seemed very promising, particularly brands using silver nano technology which costs less and has portability, zero electricity consumption and strong claims of water safety. While the data suggests that these silver nano-particles are highly effective in killing microbes, there was no data available on human safety, on consuming silver nano-particles daily over several years.

Silver is a metal that can be tolerated only in minute quantities by humans, in its ionic form. Since silver nano-particles are of recent origin, it is impossible to predict their long term impact. We cannot assume that they will behave in the same way as the traditional ionic silver.

Another leading brand of manual water filters uses chlorine to kill microbes after which the residual chlorine is removed from the water. Chlorine can react with organic matter in the water and form dangerous compounds. A number of scientists around the world believe that long-term consumption of chlorinated water increases the risk of cancer and several other ailments. While I have no data on how effective these water filters are in removing the added chlorine from the final drinking water, the mere use of chlorine put me off them.

At this stage in my research for the perfect water purifier, all the four major purification systems that are popularly sold, had at least one major drawback. To my surprise, my quest ended with a product that used technology developed by scientists at BARC. This technology can be licensed by any manufacturer and delivers a simple, effective, mechanical water-purifier that will form the subject of the next article.

The author is an environmentalist and CEO of Krya, a company that deals in products for sustainable urban living. Mail her at