An expert committee set up by the National Green Tribunal (NGT) to study the use of reverse osmosis (RO) said water supplied by municipalities from lakes, rivers and ponds does not need RO filtration.
A report submitted by the committee to the NGT on April 30 said RO plants were being installed indiscriminately without considering quality or source of raw water. The RO process separates water into two streams — purified water, and concentrate or waste stream, which contains salts, including micro-organisms.
The report said, “It is a fact that RO technology is generally not required for places having piped water supply, primarily by municipalities, from surface water sources like rivers…and ponds.”
It added that the level of total dissolved solids (TDS) found in surface water was lower than in ground water sources.
The committee recommended installation of RO plants for sources having TDS levels above 500 mg per litre (mg/l), which is the acceptable limit as per the 2012 Indian Drinking Water Standards. For sources having TDS level below 500 mg/l, the committee said ultra-filtration clubbed with UV or other disinfection can serve the purpose.
The committee was set up by the NGT on December 20, 2018, following a plea regarding utilising waste water generated by RO process. For domestic and commercial RO use, the committee recommended manufacturing RO systems that recover more than 60% of purified water, with recovery level to be enhanced up to 75% in a phased manner.
Sharad Tiwari, one of the applicants who filed a plea in the NGT, said, “In Delhi, you can see many offices and homes using RO purifying systems. There is so much wastage because of that, and that is problematic because there are some people in the city who do not get enough water.”
Dinesh Mohaniya, vice-chairman of the Delhi Jal Board (DJB), said they use a sand filtration system instead of RO. “The water supplied by the DJB across Delhi is drinkable water and it doesn’t need additional filtration of any sort,” he said.