Skip to main content

Rainwater tank performance calculator

As the cost of a domestic rainwater harvesting (DRWH) system depends mainly on the size of the tank, it is important to design the tank to ensure optimum performance at tolerable cost. This programme calculates the approximate system reliability and efficiency for a selection of tank sizes including one that you can define, using your monthly rainfall data and roof area. You can also define how the rainwater will be used by giving a nominal daily demand and choosing between three water management strategies.

By looking at the reported performance for all the tank sizes, you can change your chosen size, nominal demand and management strategy until it reaches an acceptable performance level.

Further information

More detailed information on the workings of the calculator

Help on interpreting the data

DTU research note RN-RWH04 on the statistical methodology employed in the calculator


The accuracy of results from this calculator depends on the quality of data input. The process of converting from monthly to daily data may cause errors of up to 2%. The calculator has been optimised for tropical locations so it may not model temperate climates accurately The calculator is provided in the hope that it will be useful but without any warranty. The results should be used as a guide only.


Input Data