Coffee Break Training: Access and Water Supplies: Static Water Supply Calculations [open pdf - 223KB]
"In many parts of the country, a static water supply like this quarry pond might serve as a community's major fire protection water source. There may be times, though, that an urban area fire department may have to draft from a pond or lake in the local public park if its regular water supply is disturbed by an earthquake, power loss, or other service interruption. To prepare for that contingency, the fire department should do a preincident survey to determine the amount of available water. Determining the volume in a symmetrical container such as a square swimming pool or round tank is simple: there are mathematical formulas in almost every fire protection hydraulics handbook to do the calculations."
Coffee Break Training - Fire Protection Series No. FP-2009-19
United States Fire Administration: http://www.usfa.fema.gov/