Can rain water be stored outside?

Can the surface area of a water cistern be enough to harvest rain water?

• Hi everyone, Ok so im doing some research on water tanks/cisterns and im only reading about collecting water from rain gutters or pumping it form a nearby stream. I was thinking that if you have a large enough tank/s, the surface area of that tank/s would catch enough rainwater for a small rural community of about 400-500 people. Let me set up a scenario and explain the numbers so that you can give me feedback on whether this is possible. 1. Two above ground cisterns placed higher than the village. (2 cisterns so that one can be cleaned and for other sanitary purposes) 2. Round Cisterns (or square) maybe 3 feet apart and 6 feet high: each 10 foot inside diameter with walls an extra 2 feet thick 3. This means that the two cisterns next to each other are about 31 feet long and 14 feet wide 4. Cistern Capacity will be about 2[(((pi)(5)^2)*6)*7.48]= 7050 Gallons 5. MOST IMPORTANT PART, a metal sheet with a curved edge placed over the 2 cisterns will give it an area of 31*14= 434 square feet 6. The average rain fall per year is 74in. More specifically, monthly rain fall is: (in inches) January 1.7 February 1.3 March 4.3 April 7.4 May 7.0 June 8.8 July 11.2 August 7.4 September 10.9 October 9.4 November 3.6 December 1.4 7. This means water collected over one year would be [(434 sq ft)(74 in)(600 Gallons per inch)/1000]= 19,270 Gallons Is this not enough water for a rural community of 500? And if not cant the rain harvest area above the tanks be made a bit bigger? Maybe keep the tanks the same size but extend the metal sheet so that more water can be caught and funneled into the tanks below. I know it rains less in certain months but would the community not be able to live just off the rain water? Thanks for taking the time to read all this. Give me your thoughts on whether it could work or not because i havnt seen anything onlie about just using the area of the tanks themselves to collect water. Thanks Nicolas ps( can u guess where i am?)

• Answer:

  Interesting idea Nicolas. I looked into minimum water requirements at http://www.waterencyclopedia.com/St-Ts/Survival-Needs.html and found that the minimum needed to survive is about 3.2 quarts per day per person (average person, in an average climate). The site goes on to say that each person's minimum requirement is 13.2 gallons per day for drinking, sanitation, and hygiene. Your 500 person community would require 146,000 gallons per year just to survive, and would require 2,409,000 gallons to meet minimum annual water requirements. These bare minimum numbers make it sound as if we're fish rather than humans, but there you have it ;-)