Guidance on use of rainwater tanks
Sources of chemical hazards can be divided into two types:
- Those arising from off-site sources beyond the control of the owner/resident, including urban traffic, industrial emissions and poor agricultural practices (for example, pesticide overspraying). In urban areas, potential contamination by lead has attracted most concern, due to its relatively common use, while in rural areas contamination from pesticides has been the major issue.
- Those arising from on-site sources in the immediate vicinity of the tank, and controllable by the owner/resident. These sources include characteristics of the roof catchment; materials used in construction of the roof, gutters, piping and tanks; flues from wood heaters etc.
- introduction of lead-free petrol in the 1980s and lead replacement petrol in 2002
- tighter controls on industrial emissions
- increased surveillance and control of pesticide use
- advances in design and construction of tanks and associated equipment
- development and implementation of standards relating to materials that can be used in contact with drinking water or food
- reduction of lead concentrations in paint from up to 50% before 1950 to a maximum of 0.1% from 1997
Industrial and urban traffic emissionsIn most parts of Australia, industrial and traffic emissions are unlikely to cause significant impacts on the quality of rainwater collected in domestic tanks. In addition, as discussed above, several measures have been introduced to reduce levels of airborne contamination and potential impacts on the quality of rainwater collected in tanks.
Analyses of rainwater from domestic tanks in Adelaide (Fuller et al. 1981, South Australian Department of Human Services unpublished results 1999-2002), Newcastle (Coombes et al. 2000, 2002a) and overseas (Haeber & Waller 1987) did not detect an impact on lead concentrations in tank rainwater from urban emissions.
In Adelaide, the testing of rainwater from household tanks near industrial precincts was undertaken as part of two investigations into the impacts of contaminants associated with local emissions. Lead, manganese, nickel, zinc and hydrocarbon concentrations in the rainwater samples were consistently below the guideline values cited in the ADWG (South Australian Department of Human Services, unpublished results 1999-2002).
Huston et al. (2009) investigated the atmospheric deposition of contaminants on roofs at 13 sites in Brisbane. The conclusion of the study was that elevated lead levels were most likely caused by roofing materials and only partially due to atmospheric deposition.
Notwithstanding these results, there may be localised areas where tank rainwater quality is affected by specific industries. Relatively high concentrations of lead (mean 61 µg/L) were detected in surveys of tank rainwater collected in Port Pirie, South Australia (Fuller et al. 1981; Body 1986). The source of this contamination is considered to be a very large smelter, and Port Pirie residents have been advised not to use rainwater collected in domestic tanks for drinking or food preparation.
When in doubt about the possible impact of local industry, advice should be sought from the local water authority, environmental health agency or environment protection agency.
Pesticides – agricultural pollutionUse of pesticides and potential drift from agricultural areas has been the subject of increasing public concern, and one of the issues commonly raised has been potential contamination of roofs used as catchments for rainwater tanks. There have been complaint investigations but pesticides are rarely detected and, where they are, concentrations are well below health-related guideline values (South Australian Department of Human Services, unpublished results).
In surveys of rainwater quality in rural areas, most samples did not contain detectable concentrations of pesticides (Victorian Department of Natural Resources and Environment 1997; Fuller et al. 1981; Paskevich 1992; New South Wales Environment Protection Authority and Northern Districts Public Health Unit 1996; Chapman et al. 2008). Endosulfan, profenofos, chlorpyrifos and dieldrin were detected in some samples, but all at concentrations well below health-related guideline values cited in the ADWG.
If in doubt about the use of pesticides in a particular area, advice should be sought from the relevant agriculture, environmental health or environment protection agency.
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BushfiresBushfires generate large amounts of smoke, ash and debris that can settle on roof catchment areas. In addition, it is possible that fire retardants or foams may also be deposited on roofs.
Such material can be washed into tanks, either when water is applied to the roof as part of fire protection activities, or when it rains after a bushfire. Although the presence of ash and debris in rainwater does not represent a health risk, it could affect colour, turbidity and taste. The recommended concentrations of the commonly used retardants and foams should not represent a health risk, but they may affect the taste of the water if washed into a rainwater tank.
Contaminants identified as a risk to health after a bushfire event include polycyclic aromatic hydrocarbons (PAHs) from burnt organic matter and arsenic, released during the combustion of wood treated with arsenic-based preservatives. A pilot study of 49 tanks in north-eastern Victoria after the 2003 bushfires found that levels of PAHs and arsenic were below the ADWG values (Spinks et al. 2006). Elevated levels of cadmium, iron and zinc were recorded however it was unclear if this was due to roof materials or the bushfire debris. There are no health-related guideline values for iron or zinc.
Slow-combustion heatersConcerns have been expressed about the potential impact of emissions from slow combustion wood fires on rainwater collected in domestic tanks. Public complaints have ranged from reports of a slight burnt wood taste to tainting with creosote. However, in a survey of rainwater collected from roofs incorporating wood heater flues, polyaromatic hydrocarbon (found in combustion products) concentrations did not exceed guideline values in the ADWG (Victorian Department of Natural Resources and Environment 1997).
Roof materialsRoofs may be constructed from a variety of materials such as cement or terracotta tiles, Colorbond®, galvanised iron, Zincalume®, asbestos/fibro cement, polycarbonate or fibreglass sheeting and slate. All of these should be suitable for collecting rainwater.
LeadSurveys of rainwater from domestic tanks have identified lead contamination as a potential problem. Results have been variable with exceedances of the ADWG health-related guideline value of 10 µg/L (NHMRC & NRMMC 2004) ranging from 0% to 15% of samples collected (SA Health unpublished results 1999-2009; Simmons et al. 2001; Chapman et al. 2006 and 2008; Morrow et al. 2007; Huston et al. 2009; Rodrigo et al. 2009). In addition to these results a survey in Melbourne recorded a particularly high exceedance frequency of 33% (Magyar 2008).
As discussed in other sections the reduction of lead concentrations in paint and the introduction of lead free petrol have decreased the risk from paint and general traffic emissions. However, roof materials and uncoated lead flashing in particular remain a potential source of contamination (Simmons et al. 2001; Chapman et al. 2006; Magyar et al. 2008; Huston et al. 2009), as rainwater tends to be acidic and may mobilise lead, and possibly other metals, into solution. The increasing availability of lead-free or coated lead flashing is expected to reduce future concentrations of lead in rainwater tanks.
Roof catchments used in the collection of rainwater for drinking should not include uncoated lead flashing. Alternative materials should be used in new roofs or when renovating or extending roofs. In existing roofs, painting of uncoated flashing will reduce the risk of contamination. Lead may also enter rainwater from lead washers for roofing screws. These can be replaced with plastic washers.
Leaching of lead into roof run-off may be more of a problem from poorly maintained roofs and gutters, where the process could be increased by the action of water made acidic with organic substances from materials such as leaf litter.
Preservative-treated woodPreservative-treated wood could be a source of chemical contamination if there is direct contact with rainwater that is to be collected in a domestic tank. Examples of timber preservatives used in Australia are:
- water-based preservatives, such as copper chrome arsenates (CCA) and boron compounds
- oil-type or oil-based preservatives, such as creosote
- light organic solvent preservatives, such as solutions containing pentachlorophenol.
Cement-based or terracotta tilesThe coloured surface of cement-based or terracotta tiles will oxidise over time through natural weathering. This oxidised coating may break down and be washed into rainwater tanks, thus colouring the water.
The coating is 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.
It is possible to purchase colour-through tiles that have colour impregnated throughout the tile, which is a more stable type of tile.
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Asbestos/fibro-cement roofingAlthough no longer used in new houses, asbestos may be present in some pre-1970s roofs. Although asbestos fibres are dangerous to health when inhaled in sufficient quantities, it is not believed that asbestos in drinking water poses a risk (ADWG). Asbestos is incorporated into some types of pipe used in distribution of public water supplies.
Note: Asbestos roofing material should, as far as is practicable, be left undisturbed since fibres can be released into the air by actions such as cutting, grinding or drilling. High-pressure roof cleaning methods should not be used on asbestos roofs. Where the roof catchment area has deteriorated badly, it should be replaced with asbestos-free substitutes.
Paints and coatingsBefore purchasing materials or paint for roofs used to collect rainwater, read and observe the manufacturer’s recommendations on labels and brochures. Look for warnings. If in doubt, check with the manufacturer. Three types of paints and coatings are:
- lead-based paints (including primers) – concentrations of lead in paints have been substantially reduced over the last 50 years, but care should still be taken to ensure that paints used are suitable for use in association with collecting 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.