Cistern

The cistern is the main component of a water harvesting system. Cisterns are generally made from either metal or plastic and come in a wide variety of sizes. The size of the cistern depends on rainfall and usage data and can be predicted using a computer model found here.

Gutter System

The gutter system conveys water from the roof surface to the water harvesting cistern. Often, an existing gutter system can be modified for use with a water harvesting system.

Overflow

The overflow simply allows runoff to bypass the cistern when it has reached maximum capacity.

Pump

A pump is needed whenever water must travel a significant distance or maintain a constant pressure. You can learn how to select an appropriate pump for a rainwater harvesting system by reading this factsheet.

Filtration

Varying degrees of filtration are required depending on the water's use. For most situations, a screen filter at the gutter inlet can be used to remove large particulates from the roof runoff. Devices known as first flush diverters can also be installed to prevent the initial runoff, which contains the most pollutants, from entering the cistern.

Mosquito Screen

A 1mm or smaller screen should be installed at any point where standing water could be exposed to the outside environment to prevent mosquitos from breeding within the cistern.

Secondary Water Supply

In situations where water availability is important, plumbing for city or well water can be connected to use in the event of an empty cistern. When installing a secondary water supply, it is important to consult your local plumbing codes, since there are often strict regulations to prevent the mixing of rainwater with city water supplies.