Water

Designing homes to use water efficiently, reduce costs and cope with more frequent droughts or storms.

Rainwater Systems: Design

In designing a rainwater collection system, you’ll need consider ways to minimise potential contamination of water supplies, especially if the clients plan to use it as drinking water.

Statutory requirements

The installation of individual water supplies to houses is covered by the NZ Building Code which requires premises to be provided with potable water for consumption, oral hygiene, utensil washing and food preparation. It is the responsibility of house owners to ensure that a potable water supply is provided.

A building consent is required for rainwater collection systems that are piped within a house and are in any way connected to piped mains supply system.

A building consent is also required for tanks (whether plumbed to the house or not) that:

  • exceed 2000 litres capacity and are supported not more than two metres above the ground, or
  • exceed 500 litres capacity and are supported not more than four metres above the ground.

The standard for potable water is set by the Drinking Water Standard for New Zealand 2005 which is issued by the Ministry of Health. Advice on providing safe household drinking water can be obtained from the Ministry of Health.

NZBC G12/AS1 requires backflow prevention to be provided where it is possible for water or contaminants to backflow into a piped potable water supply. The responsibility of owners and building professionals to prevent contamination of potable water supplies cannot be overemphasised.

Whatever type of storage system is used, overflow from and drainage of tanks must be to an approved drainage outlet or in rural areas a natural watercourse.

Protecting potable water supply

Approximately 10% of New Zealand’s population depends on roof-collected rainwater for drinking water. Studies show that rainwater collected from roofs and stored usually fails to meet drinking water standards and is often contaminated. Few roof-collected rainwater-linked disease outbreaks have been reported in New Zealand, but generally health risks associated with contaminated rainwater are not well defined or quantified.

All rainwater systems intended to supply water for human consumption should be:

  • designed to minimise risk of contamination
  • maintained to a satisfactory standard.

Also see Rainwater Systems: Specifying Materials and Rainwater Systems: Minimising Contamination.