Water Tanks and Different Roof Types

New Roofs

Colorbond, zincalume and galvanised steel sheeting; asbestos/fibro cement; polycarbonate or fibreglass sheeting; and slate. Regardless of the roofing material used, with new roofs it is advisable to divert the first few substantial run-offs away from the rainwater tank.

This is done to allow dust and other debris left on the roof after construction to be washed away.

NOTE: Under AS 2180 – 1986; Section 1.11 – “on completion of the installation of all guttering and roofing, all debris such as cement mortar and in particular, metal clippings and filings shall be removed”.

Where concerns exist about the suitability of a roofing material for use as a rainwater catchment surface, advice on the matter should be sought from the manufacturer.
Asbestos/fibro-cement roofing

Please refer to our seperate guide on Asbestos Roof and a Water Tank

Cement based or terracotta tiles

The coloured surface of cement based or terracotta tiles will oxidise over time through natural weathering. This oxidised coating may break down slowly and be washed into rainwater tanks, thus colouring the water.

The coating has been found to be non-toxic and, if left undisturbed, will settle to the bottom of the tank. The colour may reappear after rain if settled material is stirred up by water flowing into the tank. If this becomes a problem the tank should be drained and cleaned and roof and gutters washed down and cleaned to prevent oxidised material entering the rainwater tank.

It is possible to purchase colour-through tiles that have colour impregnated throughout the tile and which may be subject to less oxidation.

Paints and coatings

Before purchasing materials or paint to be used on roofs that will be used to collect rainwater for drinking, read and observe the manufacturers recommendations on labels and brochures. Look for warnings. If in doubt check with the manufacturer.

Lead-based paints (including primers) – are toxic and not suitable for use in association with the collection of rainwater for human consumption.

Acrylic paint – will leach dissolved chemicals including detergents in the first few run-offs after application and these run-offs should not be collected.

Bitumen-based (tar) materials – are generally not recommended as they may leach hazardous substances or cause taste problems.

Pesticide-treated wood

The use of pesticide-treated wood should be avoided where it may come into contact with rainwater to be collected in a domestic tank. Chemicals used in the preservation process may be washed from the treated wood into the tank. Examples of timber preservatives used in Australia are:

water-based preservatives such as copper chrome arsenate compounds and boron compounds
oil-type or oil-based preservatives such as creosote
light organic solvent preservatives such as solutions containing pentachlorophenol. If wooden shingles have been used it will be necessary to ensure they have not been treated with chemicals that may taint the water.
Lead flashing

Lead is a cumulative poison that can have a number of adverse effects including serious impacts on the central nervous system. In utero exposure of fetuses and exposure of infants are of greatest concern.

As a precaution lead flashing should not be used on those parts of a roof used as a rainwater catchment area. In the case of an existing roof, lead flashing should be replaced if possible. Where small quantities of lead flashing are used or retained it can be painted over with a suitable roof paint. Coated lead flashing is also available.

Leaching of lead into roof run-off may be more of a problem on poorly maintained roofs and gutters where the process may be increased by the acidic action of water containing organic substances leached from materials such as leaf litter.

Industrial pollution

There is an increased risk of pollution by airborne contaminants in major urban centres and industrial areas. Collection of rainwater for human consumption (drinking and cooking) in areas affected by heavy traffic, industry, incinerators and smelters is not recommended.

In Port Pirie, South Australia, for example, there is a long history of smelting with associated airborne lead pollution and analyses of rainwater collected in domestic tanks have detected concentrations of lead exceeding drinking water guidelines.

When in doubt about the possible impact of local industry advice should be sought from the local authority, environmental health authority or environment protection authority.

Agricultural pollution – pesticides

Although the use of pesticides is coming under increasing scrutiny and control, rainwater collected in some agricultural areas may be subject to contamination by pesticides or other chemicals. Aerial spraying provides a greater potential for contamination.

In surveys of rainwater quality in rural areas pesticides were not detected in most samples. Endosulfan, profenofos, chlorpyrifos and dieldrin have been detected in some samples but all at concentrations below Australian Drinking Water Guidelines. There was evidence that tanks included in the surveys were poorly maintained. The risk of pesticide contamination could be reduced by appropriate maintenance and by the use of first flush diversion devices.

If in doubt about the use of pesticides in the general area, advice should be sought from the local authority, Department of Agriculture, environmental health authority or environment protection authority.

Wood burners

There have been consumer reports of contamination, including tainting with creosote, of rainwater collected from roofs that incorporate flues from wood burners. While a range of hydrocarbons could be deposited on roofs in the vicinity of such flues limited testing in one survey (Victorian Department of Natural Resources and Environment, 1997) did not detect concentrations exceeding guideline values in the Australian Drinking Water Guidelines. Nevertheless, it is suggested that where possible rainwater should not be collected from that part of a roof that incorporates a flue from a wood burner.

In addition extra care should be taken to operate wood burners correctly and to only use appropriate fuel.

Related posts:

1. Water Tanks and an Asbestos Roof
2. Types of Rain Water Tanks
3. What Size Water Tank?
4. A Health Guide to Your Rain Water Tank
5. Installing a Water Tank