News of the monsoon arrival in Goa always brings flashbacks of powerful thunderstorms, strong winds and persistent rains coming downin sheets running in rivulets on the ground, flooding seasonal ponds and nearby rice fields. Goa receives an averageof 2.86 Meters of rain per year.With an area of 3700 square kilometers and an estimated population of 3 million people in2017, this works out to about 3.8 Million Liters per year perresident.With adequate capture and storage as well as prudent management of this bounty, there should be plenty of good drinkingwater to meet the needs of the inhabitants of Goa. Nearby Chennai in Tamil Nadu on theother hand, receives about 1.27 Meters of rain per year which is insufficientto meet the needs of its estimated 9 million inhabitants. Chennai uses waterfrom surface sources and underground aquifers which get eventually depleted. The minimum amount of water aperson needs for drinking and sanitation is estimated to be 20 Liters perday although, unfortunately, there are people who have to subside on lesswater.The total amount of water that is tobe used to produce the goods and services consumed by one person per yearin India is estimated to be about 1 Million Liters. For reference theglobal average is estimated at 1.243 Million Liters. By various estimates two thirds ofthe people in the world lack adequate drinking water.About 1percent of the total water in the world is drinkable. The best strategy known,to convert sea water into drinkable water, is desalination by ReverseOsmosis (RO), wherein the seawater is pumped at pressures exceeding 8000Kilo Pascal through Polyamide thin film composite membranes designed to separate the bigger mineralmolecules from the water molecules. Chennai uses the RO desalinationprocess to supplement the drinking water requirements of its inhabitants.One such RO plant at Minjurwas designed to output about 100 Million Liters per Day (MLD) of drinking waterat a projected cost of approximately 4.5 paise per liter . As a reference the Carlsbad waterdesalination plant, supporting the San Diego County in California, USA outputs190 MLD at a projected cost of approximately 10 paise per liter. Further cost reductions in desalinated water processing are expected to result from the use of cheaper solar energy and more efficient graphene oxide membrane technology. There are thousands of desalinationRO plants in the world, helping meet the ever increasing shortages of drinkingwater. The largest plant near Riyadh, at RasAl Khair was designed to output 728 MLD. The one at Sorek in Israel was ratedat 627 MLD.An attractive feature of the desalination plants is the predictability of the sea water supply.
In Goa the rains should providesufficient, good, clean water for the foreseeable future but a desalination plant may be needed as the population pressures on the current supplies increase. Note: reference data gleaned from published sources is subject to many variables such as labor costs, energy costs, currency fluctuations etc.
