The National Green Tribunal on May 28, 2019 asked the ministry of environment and forests to issue a notification prohibiting the use of RO in areas when the Total Dissolve Solid (TDS) level was below 500 mg/l to ensure less wastage of water.
- The order added that in places where use of RO is allowed, a condition must be enforced that 60% of the water will be recovered. Later, this threshold should be stepped up to 75%.
- The order also said that the water that goes waste should be used for the purpose of washing utensils, flushing, gardening, cleaning of vehicles and mopping of floors, the order added.
- NGT’s directions came after a report by National Environmental Engineering Research Institute, Central Pollution Control Board and IIT-Delhi stated that RO is meant only for treating dissolved solids and, according to BIS standards, drinking water is considered below par only if TDS is above 500 mg/l.
- While criticising RO manufacturers the report says that RO manufacturers should provide labelling on the purifier specifying that the unit should be used if TDS is more than 500 mg/l.
- Application of RO in developed countries is limited to desalination, that is, producing drinking water from high TDS containing seawater (which is salty). The growing use of this technology in treating low TDS water is the new normal in India.
- However, the Delhi Jal Board said that the most of the water supplied to Delhi comes from Yamuna and river origin raw water does not have very high TDS levels all over the country. The problem is limited to only those places where water is supplied from borewell sources. Drain No. 6 coming from Haryana also has high TDS while the 80 MGD of water that comes from borewells might too have a similar issues.
- The official pointed out that some housing societies were illegally using borewells to mix groundwater with DJB water. “In a bid to avail water subsidy under the 20KLD scheme, some residents in upscale areas use borewell water which costs much less. In case of such blending, the final mixed water will have high TDS values of 1500-1900,” said the official.
- Experts say TDS is not the only parameter for clean water. “The water could have a TDS of 350-400 mg/l but it won’t necessarily be clean. The water needs to have the right ions, pH level and essential nutrients,” said Vikram Soni, an ecologist and physicist, who specialises in water.
- The tribunal also directed to sensitise public about the ill effects of demineralised water and asked the government to make it mandatory to recover more than 60 per cent water wherever RO is permitted across the country.
What is Reverse Osmosis
- Reverse Osmosis (RO) is a water treatment process that removes contaminants from water by using pressure to force molecules through a semipermeable membrane.
- In the process, it also removes minerals beneficial to our health from the water — although most RO manufacturers say their machines re-introduce minerals in the purified water.
Total Dissolved Solids
- 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 principal constituents are usually calcium, magnesium, sodium, and potassium cations and carbonate, hydrogencarbonate, chloride, sulfate, and nitrate anions.
- The presence of dissolved solids in water may affect its taste.
- The palatability of drinking water has been rated by panels of tasters in relation to its TDS level as follows:
- Excellent: less than 300 mg/litre;
- Good: between 300 and 600 mg/litre;
- Fair: between 600 and 900 mg/litre;
- Poor: between 900 and 1200 mg/litre; and unacceptable, greater than 1200 mg/litre .
- Water with extremely low concentrations of TDS may also be unacceptable because of its flat,
insipid taste.
