[Answered]Explain, what reverse osmosis (RO) systems are and how do they work? Why does the Environment Ministry want to regulate RO-based water filtration systems?

Reverse Osmosis system is a technology that removes contaminants from water by using pressure to force water molecules through a semipermeable membrane (reverse osmosis). During this process, the contaminants are filtered out and flushed away, leaving clean, drinking water.

Mechanism of working of RO systems:

1. High external pressure: It works by using an external high-pressure pump to increase the pressure on the salt side of the RO.
2. Semi-permeable membrane: The pressure forces the water across the semipermeable RO membrane, leaving around 95% to 99% of dissolved salts behind in the reject stream. This is the essential principle of an RO system.
3. Salt concentration: The amount of pressure required depends on the salt concentration of the feed water. Higher the concentration of salt, higher is the pressure required.
4. Activated carbon components: It uses activated carbon components, such as charcoal and carbon black that can filter out contaminants as well as organic substances such as bacteria.
5. Cross filtration: To avoid build-up of contaminants, cross flow filtration is used that allows water to remove contaminant and also allow enough turbulence to keep the membrane surface clean. An RO membrane rejects contaminants based on their size and charge and provides desalinated water.

Why does the Environment Ministry want to regulate RO-based water filtration systems?

1. Wastage: In making tap water pass through multiple stages of cleaning, RO systems end up wasting a lot of water. Anywhere between 3-5 times more water is wasted.
2. Remove beneficial minerals: Another concern with RO is that it filters out calcium, zinc, magnesium, which are essential salts needed by the body. Drinking such water over time could be harmful.
3. Risk of infection: The National Institute of Virology claimed that most filtration methods did not eliminate Hepatitis E virus, posing a high risk of infection.
4. Contamination risk: Also, the devices which purify water for drinking purposes need to use parts that are food grade. There could be contamination from the device as well, most common being dissolution of plastics and metals in the highly purified (active) RO water.

In May 2019, the National Green Tribunal has asked MoEFCC to frame rules for the use of RO filters and also banned the use of RO purifiers in locations where total dissolved solids are low. RO systems definitely lead to water wastage. Thus, its regulation is necessary in order to save water and prevent the developing situation of water crisis. It is also important that the government must ensure the quality of drinking water in most of the states.