Necessity of RO

Background

Less than 50 percent of the population in India has access to safely managed drinking water. Chemical contamination of water, mainly through fluoride and arsenic, is present in 1.96 million dwellings. Excess fluoride in India may be affecting tens of millions of people across 19 states. Worryingly, excess arsenic may affect up to 15 million people in West Bengal.

How it works: OSMOSIS & REVERSE OSMOSIS

Osmosis is the movement of any solvent (usually water) from a region of low concentration to a region of high concentration when separated by a semipermeable membrane (which allows movement of the solvent but not the solute).

Therefore, it would happen because of some force, this is known as osmotic pressure.

 

But if there is external pressure, the pressure applied should be enough to overcome the osmotic pressure so as to forcibly remove water to one side of the semi-permeable membrane leaving the solutes on one side.

Therefore, we have simply pure water on the other side.

This is known as reverse osmosis or RO.

The bad side of RO

RO technology is not applicable to all water types.

Even the Indian water purifier industry admits this.

RO cannot be universally applicable for all water types due to key technology limitations.

The process of reverse osmosis eliminates only chemical contaminants from the water.

The RO process gives a free pass to all biological contaminants i.e. bacteria and viruses in the water.

It’s all about the TDS

RO water purifiers are effective on this count, especially in places where pesticide use contaminates groundwater (states such as Punjab) The Bureau of Indian Standards prescribes TDS of 500 mg/litre as acceptable. On the other end of the spectrum, water with low concentrations of TDS may also be unacceptable because of its flat, insipid taste.

Bengaluru’s case

Bengaluru's water was well within the prescribed range even before treatment and increased marginally after treatment. A 2015 study that tested the city's water for pH (acidic-alkaline value) and TDS found that 82.66 percent of the total samples were below the permissible TDS range. "Central region of Bangalore demonstrated 100% potability, east and west regions showed >90% of the same, whereas south-east was poorest of all with 63.88%".

Water wastage

For every one litre of potable water, RO water filters push out three to four litres of water, as per broad estimates. This 'reject' water is saline as it has a higher concentration of chemical contaminants. Saline water cannot be used to flush the toilet, swab floors, or wash cars. It will eventually find its way into the ground, contaminating everything along the way. In the long term, this will not only impact groundwater quality, but also soil and agriculture.

Stories of RO

Here is a RO Filter at Thoredoddi Government High School

The Rejected water is being collected in buckets and used for watering plants in the garden

Here's another picture where RO Rejected Water is used as a water source for the washing machine

These ideas cannot be implemented everywhere as TDS levels of water differ from place to place.

The ideal solution would be using a filter to treat the rejected water. Through this, the water can be effectively managed and reused.

Refer to the presentation for an overview 

References:

• https://greencleanguide.com/why-you-shouldnt-buy-an-ro-water-purifier/

• https://www.deccanherald.com/opinion/ro-purifiers-less-of-a-solution-more-of-a-problem-785488.html

• https://www.unicef.org/india/what-we-do/clean-drinking-water

- Rohith, Shivani, Sadhana

The bad side of RO :