Most urban households use a system of reverse osmosis (RO) to purify water before drinking. Several societies have even opted for in-house RO plants to serve potable water to residents. But there is one problem — ROs waste water.
Nitya Jacob, water expert and author of Jalyatra: Exploring India's Traditional Water Management Systems, says, “If the TDS value of the water being supplied is in the safe range, it can safely be consumed without an RO. However, if an RO is used to further purify it, we are wasting water for no reason. About 50-90 per cent of supplied water goes to waste this way.”
Environment Quality Management Consultant, Arvind Rudra says, “When we use RO to filter good-quality water we waste a lot of water.”
Rudra further explains, “The higher the TDS, the more is the impurity level of the waste water. For example, if we filter a water sample with a TDS value of 4,000, the treated water will have a TDS of around 400 and the waste water will have a cumulative TDS value of 7,600.”
The drinking water supplied by Delhi Jal Board (DJB) to Dwarka has a TDS (Total Dissolved Solids) value of about 150, which is within the permitted range specified by *WHO.
So why are ROs being used to further filter this water?
According to sources, more than 50 per cent of Dwarka's societies are equipped with in-house RO plants. Residents say there is a gap between demand and supply from DJB. Many households don't get enough water supply from DJB and are left with no choice but to use ROs to make underground water usable.
Advocate PS Singh, former secretary of Rajasthan Society, Sector 4, says, “We have a common RO plant since 2005, which is used to treat hard ground water [TDS 4,000-5,000] and supply it to families. DJB does supply potable water, but it's not enough for the number of families we have in the society.”
New Millennium in Sector 23 also faces a similar problem and is compelled to use the society RO.
But what about places where DJB supplies adequate drinking water?
A quick recce of Dwarka revealed that most DDA and CGHS flats used individual kitchen ROs to treat the water supplied by DJB. A society, on average, uses 50,000 to 1,00,000 litres of water every day. Those equipped with an in-house RO plant also expels an equal amount of water as waste. At present, more than 100 societies in Dwarka have RO plants.
Anil K Mishra, assistant bacteriologist quality control, DJB, says, “The water we supply is potable and fit for drinking. Running this water through another level of purification only causes water wastage. It also decreases the mineral content of water, which is essential for the human body. So unless the water supplied is contaminated, it should not be further treated by an RO. We collect 500-600 samples every day to check whether the water is contaminated. It is imperative that people understand that using an RO where it is not required is unwise.”
*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 1,200 mg/litre; and unacceptable, greater than 1,200 mg/litre.
According to IS 10500 : 2012 (BIS 2012), the acceptable limit for TDS is 500 mg/litre. The permissible limit in the absence of alternate sources is 2,000 mg/litre.
