Treating drinking water for flouride, arsenic and salinity

Many people in India lack access to a safe and reliable source of drinking water. Water borne diseases are common in many areas, and are the result of contamination of water sources, but geology is also a constraint to clean water. High levels of flouride, arsenic and salts are naturally found in many aquifers throughout the country. These can cause both acute and chronic health problems, and in some cases the ground water is not even potable.


Reverse osmosis (RO) is one of the options for treating contaminated water and has been used to provide drinking water in rural areas (www.Sarvajal.com is a great example and deserves its own blog post... we'll get to it one of these days). The challenge with RO is that there are some high costs associated with initial investment and maintenance. Waste water is also a problem as over half of the water treated may be lost as waste. In areas where total dissolved solids (TDS) are high treatment efficiency may be as low as 30%, what does one do with the remaining 70% of salty water? We visited one location in the Mehwat District of Harayana where salts in the shallow aquifer exhibited a TDS of over 30,000 parts per million (ppm). That's more salty than seawater!

An alternative to RO is solar distillation which relies on the sun's energy to evaporate water, leaving the impurities behind, where the vapor is condensed and collected as pure water. Its so pure that salts or minerals need to be added- it turns out that humans need a minimum TDS as well. The other issue with solar distillation is capacity. The type of unit pictured here (built by IRRAD) produces about 4 liters of water per day for every 1 square meter of surface area. IRRAD is testing an approach to use a parabolic reflector to harness more of the sun's energy to increase evaporation and therefore increase capacity but it is still under testing.

There apparently are a few other technologies to treating for arsenic, flouride or salts but we have yet to visit any in action. It is on our list however.

Another approach entirely is to identify new sources of water. For example, finding fresh water pockets in the aquifer nearby, or rainwater harvesting. More on this in a future post.