The system wastes water, and is expensive

According to industry estimates, 5.2 million households use water purifiers of which about 42 per cent (or 2.1 million households) employs RO. Assuming every household has 5 members;

Total water consumed = 21 million litres per day (mld) (if per capita consumption is 2 litres each for drinking and cooking which is a very conservative)

At 60 per cent reject ratio (best case scenario), 52.5 million litres of water needs to be fed to receive 21 mld purified water; 31.5 mld water (or 3 litres per capita) is wasted

Industry sources say that operation and maintenance cost of RO filters @ Rs 20-30 per kilolitre = Rs 4-6 lakh per day (@ 2lpcd)

In other words, annual maintenance = Rs 15-Rs 23 crore (for consuming 2 lpcd)

This is besides the municipal water bill if your house is connected

There is also a debate on RO removing essential salts and nutrients from water.