The The spreadsheet is divided into four panels. The first simply shows the values of two constants: gallons per cubic foot (7.481), and the volume of water per inch of rain that falls on a square foot of roof (7.481/12 = 0.623): The second panel allows the user to set a series of variables related to the storage tank and roof characteristics of a specific rainwater collection site, as well as the volume of daily water use. Note that values can be entered only for those variables that are The third panel gives the relationship between water level and volume for the tank dimensions entered in the Site variables panel. Also given are (1) an estimate of the number of days that the calculated volume will last, given the daily water use; and (2) the amount of rainfall needed to fill the tank(s) to capacity for the given site variables: The last panel gives estimates of the volume of water collected and stored per rainfall amount, as well as an estimate of the number of days of water use resulting from the amount of water saved from this rainfall: Note that it is assumed that multiple tanks are all the same size and are sited on the same level; if they are not, analyze each tank separately.
Updated 20 June 2011 |