Guidance on use of rainwater tanks

4. Identifying potential hazards and health risks (systematic analysis)

Page last updated: March 2011

Assessment of the health risk of rainwater tanks requires consideration of whether a hazard to human health is present and whether the dose of the hazardous material is sufficient to cause illness.

Both the concentration of the hazard and the degree of exposure determine the dose (of hazardous chemicals and pathogenic microorganisms).

The most common use of rainwater tanks in Australia is to provide a private source of drinking water to individual households. This use provides the highest level of exposure compared to other domestic and gardening uses. Use of rainwater for purposes other than drinking is discussed in Section 2.

Rainwater tanks are also used as a source of public or community-based drinking water supplies. This type of use requires consideration of broader legislative or duty-of-care requirements and is discussed in Section 11.

Collection and storage of rainwater introduces the potential for chemical, physical and microbial contamination. The most common hazards in water sources obtained from surface catchments worldwide, including roof run-off, are microbial pathogens of faecal origin (enteric pathogens). In most of Australia (exceptions are discussed below) chemical and physical quality of rainwater is relatively easy to maintain, but microbial quality is more difficult to manage. This is supported by investigations of rainwater quality as discussed below.

Systems incorporating buried pipework (so called ‘wet systems’) are becoming increasingly popular to maximise yields from multiple gutters and where rainwater is plumbed into homes. Buried pipes can be susceptible to cross-connection and external contamination as well as potential impacts on aesthetic quality due to stagnation.

Rainwater tanks can also represent a health risk by providing breeding sites for mosquitoes.