How to calculate the volume of a storage tank based on a certain annual rainfall ?

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How to calculate the volume of a storage tank based on a certain annual rainfall. I need technical information on rain water collection for my project.

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3 Answers

  1. Rainwater harvesting

    Important is  to determine the volumes people use for drinking and cooking (say between 2-5 litres per capita day (lcd)) and that for other purposes (say between 10-20 lcd). Using those figures and the number of people you can calculate the amount of water you need per day or month. If you have to collect those volumes all from rainwater  then you can calculate the required surface area and the required storage capacity. Each surface area has a specific runoff coefficient, i.e. the efficiency of collection or the rainfall minus the wasted water. For hard roofing materials the coefficient is between 05-0.9, which means that of each litre of water fallen on the roof you can collect between 0.5 -0.9 litres! For ground surface areas this coefficient is much lower, depending on soil type and condition: usually between 0.10 and 0.25. The simplest way to calculate is cumulating the required monthly volume of water (drinking/cooking) in a diagram, and plot the volume of water required to satisfy this demand. Demand drinking and cooking Q = number of consumers * C1 * 30 = Q [m3/month] C1 = daily water consumption for drinking/cooking per capita (say 2-5 lcd) Demand other purposes Q = number of consumers * C2 * 30 = Q [m3/month] C2 = = daily water consumption for non- drinking/cooking per capita (say 10-20 lcd) You can then calculate (from the graph, see for an example of this graph theWELL fact sheet on domestic rainwater harvesting).