Harrison Grierson was commissioned by Greater Wellington
Regional Council (Greater Wellington) to develop a model of
rainwater tanks in the urban environment for the cities in the
Wellington region; Lower Hutt, Upper Hutt, Porirua and
Wellington.

This report presents the findings for Porirua and discusses the
costs of installing rainwater tanks. The model is set up to
calculate the volume of water in the tank each day using the
rainfall over the roof area as the flow into the tank and the
household demand as the flow out of the tank. The tank was
assumed to supply only outdoor usage and toilet flushing.