Rainwater tanks are available in a range of suitable materials including galvanised steel, Aquaplate™, Zincalume™, fibreglass, plastic and concrete. All can be suitable, providing the materials used are at least of food-grade standard (for example, plastics should comply with AS 2070) and preferably comply with the requirements of AS/NZS 4020 Testing of products for use in contact with drinking water.
New rainwater tanks can impart specific tastes and odours. For example, galvanised tanks can impart a metallic taste when first filled, due to leaching of excess zinc.
New concrete tanks can release excess lime, leading to a high pH (Gee 1993; Simmons et al. 2001) and possibly a bitter taste. Rainwater from other types of tanks tends to be slightly acidic (Simmons et al. 2001). Although results outside the recommended pH range of 6.5-8.5 (ADWG) have been recorded, they are unlikely to have a direct health impact, but low pH in particular could cause increased corrosion and result in dissolution of metal tanks, pipes and fittings. By way of comparison, orange juice and some soft drinks have a pH below three.
Other types of tanks can also impart tastes related to their manufacture or the materials that they are made of but, providing the materials are of food or potable water grade, these will not represent a health hazard and will diminish over time as the tank ages. If tastes make the water unpleasant to use, new tanks may need to be flushed with water from the first fill and used for non-potable purposes until the taste of the water improves.
It has been suggested that galvanised metal can include low levels of lead, but, as discussed in the section on roof materials above, specific surveys have not detected elevated concentrations of lead associated with metal tanks.
Australian and Australian/New Zealand Standards that apply to tanks and their associated fixtures and fittings are:
- AS 2070 Plastics materials for food contact use
- AS/NZS 2179 Specifications for rainwater goods, accessories and fasteners
- AS 2180 Metal rainwater goods – selection and installation
- AS/NZS 3500 National plumbing and drainage code
- AS/NZS 4020 Testing of products for use in contact with drinking water
- AS/NZS 4130 Polyethylene (PE) pipes for pressure applications.