Rainfall

Waiheke residents depend on rain harvesting as there is no water reticulation on the island. Water is collected off the roof and stored in tanks. These range in size but a typical modern house would have at least one 5000 gallon (22500 litre) tank.

NIWA and the NZ Meteorological Service have a long-term rainfall monitoring site at Awaawaroa Bay on Waiheke Island. Mean annual rainfall in the Awaawaroa Valley is approximately 1,280mm Source Auckland Water Resource Quantity Statement 2002

For every square metre of roof each millimeter of rain will deliver one litre of water into the tank. Hence with an annual rainfall of 1,280 mm and assuming a 100sqm roof an average house will expect to collect 128,000 litres of water in a year. This allows 350 litres per day. The average household usage in the Metrowater catchment area is 501 litres per day. Source Local Government and Environment Committee submission on water charges It is believed that Waiheke water usage is as low as 100 litres per day per person.

The flaw in this calculation is that during winter months a lot of the collected water is lost as the tanks overflow. Many Waiheke residents have to buy in water from one of the water delivery companies on the island. These companies draw bore water from the Waiheke aquifer.

Rain this year

Data source Waiheke Weather Network rain gauge Onetangi