Why are RO water purifiers being prohibited?

Homes have been effectively prohibited from installing domestic reverse osmosis (RO) systems by the Union Environment Ministry. The Ministry has issued a draft notification that seeks to regulate membrane-based water filtration systems. A membrane is a barrier that allows certain substances to pass through while blocking others.
The regulation will be in areas where the source of water meets drinking water norms of the Bureau of Indian Standards. However, studies show that the existing quality of piped water is deficient in much of India.
The Ministry was acting on a National Green Tribunal order. The order asked to prohibit use of RO purifiers where total dissolved solids in water are below 500 milligrams per litre.

RO was originally a technology devised to desalinate sea water. It uses “activated carbon” components, such as charcoal and carbon black. These components can filter out contaminants as well as organic substances such as bacteria. It all depends on the filtering material and the number of filters that incoming tap water must pass through.

In making tap water pass through multiple stages of cleaning, RO systems end up wasting a lot of water.