Rainwater harvesting: TTT

Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system could be integrated into a site plan using STEP's Treatment Train Tool. This tool provides a graphical user interface and simplified inputs on the EPA SWMM model. It is free to download, click image above. In a typical configuration:

Surface
Catchment (roof)	100% impervious
The rainwater harvesting system would be a 'Storage' Element with the following properties:
Storage type	No removal
?	Lined
Underlying soil	Doesn't matter
Evaporation factor	0
Suction head (mm)	0
Saturated conductivity (mm/hr)	0
Initial soil moisture deficit (fraction)	0
The dimensions of the rainwater cistern can be placed into the fields: Bottom elevation (m) Maximum depth (m) Initial water depth (m) The Curves table is designed to accommodate ponds of roughly conical dimensions. A rainwater cistern is usually cuboid or cylindrical in shape, so that the area (m2) will remain the same throughout the depth.

Tank used to store rainwater (typically roof runoff) for later use.

Rainwater harvesting.

Sustainable Technologies Evaluation Program

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

Abiotic transfer of water vapour to the atmosphere.