The Union government's new draft notification on regulating reverse osmosis (RO) purifiers contradict directions by the National Green Tribunal (NGT), which had sought such a notification to curb indiscriminate use of ROs.
The May 2019 NGT order, had clearly stated that ROs should be prohibited where TDS (total dissolved solids) in water was less than 500 miligram per litre (mg/l).
It had asked the government to redesign the RO system in a way that treated water would have a minimum 150 mg/l TDS concentration.
The draft notification issued February 3, 2020 by the Union Ministry of Environment, however, does not mention such limits.
Instead it only mentioned that use of membrane-based water purification system, mainly RO purifiers, shall be prohibited where drinking water complies with the Bureau of Indian Standards (BIS).
Whether or not a particular sample of water is BIS-compliant depends on several parameters, not just TDS. Whereas, the RO technology is limited to the removal of excess TDS and won’t work in cleaning other impurities or metals in water.