Rainwater harvesting/Rainwater harvesting calculators

In the design phase of rainwater harvesting system, questions will arise as to how to properly size all the equipment. Depending on how the project was contracted and who is building the system, a combination of mechanical, civil and other building engineers may be involved in the sizing and spec'ing of equipment to be installed in the system.

In response to make the decision making process easier, calculators and equations have been created for sizing rainwater harvesting system equipment, especially for rainwater tanks. The sizing of a rainwater tank can depend on the specific environmental variables such as frequency and seasonal variation of rainfall intensity, and end-use requirements such as building occupancy and peak-flow requirements.

According to a document from the EPA in 2013, the effectiveness of a rainwater harvesting system based on stormwater runoff management, adequate volume for stormwater retention must be ensured through consistent and reliable demand. One way to calculate the optimum tank or cistern for this kind of scenario would be to compare the cost of the system, or the rebate received through applicable runoff reduction credits versus the reduction in overflow frequency for a certain size storm.

Tank Performance Calculators
The University of Warwick, England provides a tank performance calculator, created by the Domestic Roofwater Harvesting Programme at the School of Engineering. The calculator can be found here.