Guidance on use of rainwater tanks

Minimising contamination by harmful microorganisms

Page last updated: March 2011

Preventive measures to reduce contamination by potentially harmful microorganisms are predicated on minimising the impact of faecal waste. As indicated in Table 2 measures could include:

  • keeping roof catchments clear of overhanging vegetation as branches provide roosting points for birds and can provide access for small animals such as rodents, cats and possums
  • preventing access by small animals and birds into rainwater tanks by screening all tank inlets and overflows, keeping access hatches closed and by maintaining the integrity of tank roofs
  • preventing entry of surface run-off from areas other than the roof catchment into below-ground tanks. Roofs should be secure and the sides and bottom of tanks should be sealed to prevent ingress
  • ensuring that buried pipework is impervious and suitable for contact with water. It should be separated from pipework carrying septic waste or sewerage.
Swimming in storage tanks should be prevented, as this type of human access can greatly increase risks of contamination.
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Table 2: Sources of potential health hazards and preventive measures
Health hazardCausePreventative measureMonitoringCorrective action
Faecal contamination from birds and small animalsOverhanging branches on roofPrune tree branches.
Install first flush device.
Check tree growth every six months.
Check device after rainfall.
Prune branches.
Empty contents of device after rainfall.
Animal access to tankProtect all inlets, overflows and other openings to prevent entry by small animals and birds.Check access covers are kept closed. Check inlets, overflows and other openings every six months.Repair gaps. Secure access cover. If animal access suspected disinfect tank using chlorine.
Maintain integrity of tank roof and body to prevent access points.Check structural integrity of tank.If a dead animal is found, empty and clean tank. If this has to be delayed, remove animal remains and disinfect tank using chlorine.
Faecal contamination from humans (above-ground tanks)Human access to tankPrevent access. Ensure tank is roofed and access hatches are secured.Check access covers are secured, particularly in hot weather.Secure access cover.
Faecal contamination from humans and livestock (below-ground tanks)Surface water ingress into tankEnsure tank is protected from overground flows and tank walls are intact.Check structure annually and that surface water does not enter during storm events.Repair or increase barrier to surface water flow. Repair or line inside of tank.
Faecal contamination from humans (buried pipework)Ingress of contaminated water, potential cross-connectionsEnsure that pipework is protected from cross-connections, that pipework is impervious and is separated from septic and sewage pipes.Remove cross-connections, repair or replace pipework.
MosquitoesAccess to stored waterProtect all inlets, overflows and other openings with mosquito-proof mesh.Inspect water for presence of larvae at least every six months (in northern areas of Australia this should be done more often).Repair screening of inlets and openings to prevent access and if larvae are present, to prevent escape of mosquitoes.
Treat tanks with a small amount of kerosene or medicinal paraffin.
Lead contaminationLead based paints and primers on roofsDo not collect rainwater from roofs painted with products containing high lead concentrations (for example, pre-1970s paint).
When painting roof, check suitability with paint retailer.
Uncoated lead flashing on roofsPaint existing material or use pre-coated products.Inspect roof and gutters every six months.Use coated lead flashing or alternative materials on new roofs. Paint existing uncoated flashing.
Increased corrosion of metals due to low pH from long periods of contact between rainwater and leavesKeep gutters clean. Install leaf protection devices on gutters.Inspect gutters every six months.Clean gutters. If large amounts of leaves are detected on regular inspections clean more often.
Chemical contaminants from tanks, pipework etcWater standing in metal pipes overnight or longer periodsUse plastic pipesInspect plumbing to identify pipe materialsFlush pipes in the morning for long enough to bring new water from the tank (several minutes).
Re-suspension of accumulated sedimentRegularly clean tank to remove accumulated sediment.
Reduce amount of sediment by keeping roof catchments and gutters reasonably clean. Protect inlet to tank using a leaf filter. Install a first flush diverter.
Inspect tank every 2-3 years.
Inspect roof and gutters and inlet filter every six months.
Clean tank if required.
Clean roof, gutters and inlet filter as necessary. Ensure filter is in place.
Other contamination from roof materialsPreservative-treated wood
Bitumen based materials
Do not collect rainwater from roofs covered with exposed treated wood.
Do not collect rainwater from roofs with bitumen-based products.
Inspect roof before installing tank.If treated wood present it could be sealed or covered to prevent exposure to rainwater.
Chemical contaminants from tanks, pipe work etc.Inappropriate material that does not comply with Australian or Australian/New Zealand Standards relating to food grade products or products for use in contact with drinking waterUse only approved materials.Check suitability of product with retailer or supplier.Remove or replace product.
Dangerous plantsOverhanging branches (check identity of suspect plants with horticulturist)Prune tree branches.Check tree growth every six months.Prune or remove plant.
DrowningAccess to tank roof
Hatches open or roof in poor state of repair
Prevent access to tank roof by children.Check access covers are kept closed and roof is intact. Ensure that trellises and trees do not allow ready access to tank roofs.Repair gaps. Secure access cover. Prune tree branches.
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Table 3: Sources of aesthetic hazards and preventive measures
Aesthetic hazardCausePreventative measureMonitoringCorrective action
Sulfide/rotten egg/sewage odoursAnaerobic growth in accumulated sediment at the bottom of tanksRegularly clean tank to remove accumulated sediment.Inspect tank every 2-3 years.Clean tank if required. If cleaning not practical (for example, in the middle of summer) disinfect tank with chlorine and flush chlorinated water through all pipework.
If practical, pumping air into the tank, to add oxygen to the water, may also help to minimise tastes and odours.
Slimes and stagnant water in pipe work Avoid u-bends or underground pipework that can hold stagnant water. Install drainage points on buried pipe work.
Musty or vegetable type taste and odours (no light penetration)Accumulated material on roofs and gutters. May possibly include pollenRemove overhanging branches from trees. Keep gutters clean. Install leaf protection devices on gutters.Inspect gutters at least every six months.Clean gutters. If large amounts of leaves (or pollen) are detected on regular inspections clean more often.
If practical, pumping air into the tank, to add oxygen to the water, may also help to minimise tastes and odours.
Coloured waterAccumulated damp leaves in gutterKeep gutters clean. Install leaf protection devices on gutters.Inspect gutters at least every six months.Clean gutters. If large amounts of leaves are detected on regular inspections clean more often.
Coloured water, particularly after rain (tiled roof)Coloured coating from tiles washed into tanks. Re-suspension from sediments when fresh intakeUse colour-through tiles.Inspect water after rainfall.Remove sediment by cleaning the tank.
Musty, vegetable or fishy type taste and odours (light penetration)Algal growth due to light penetration into tank or pipe workMake sure tank is completely roofed and is impervious to light.Inspect water every six months.Repair roof.
If practical, pumping air into the tank, to add oxygen to the water, may also help to minimise the tastes and odours.
Ensure pipework, including inlets to tanks, are impervious to light (white pipes can allow light penetration).Paint pipework with dark colour.
Bitter taste (concrete tanks)
Metallic taste (galvanised tanks)
Plastic taste (plastic tanks)
New tankUse water from first fill for non-potable purposes. Taste will diminish in subsequent fills.Water quality/taste will improve with tank age.Use water from first fill of new tanks, or water collected from newly painted roofs for non-potable purposes. Problem will diminish with time.
Detergent taste or water frothingNewly painted roofDo not collected water from first 2-3 rain events after painting.Water quality/taste will improve with paint age.Use water from first fill of new tanks, or water collected from newly painted roofs for non-potable purposes. Problem will diminish with time.
Hydrocarbon or preservative taste Deposits from wood combustion heater flueInstall flue in accord with Australian Standards. Operate heater correctly.
Use appropriate fuel (not preservative treated).
Check flue installation. Check operation of heater and choice of fuel.Repair flue. Discard inappropriate fuel.
Insects/water boatmen etc.Access to stored waterProtect all inlets, overflows and other openings with insect proof mesh.Inspect water for presence of insects and/or larvae every six months.Repair screening of inlets and openings to prevent further access.
Use simple coarse filter to remove remaining insects.
Small white flakes in waterMicrobial growthKeep gutters clean. Growth encouraged by nutrients contained in plant and soil material accumulated in gutters or at the bottom of tanks.
Install leaf protection devices on gutters
Inspect gutters at least every six months.
Inspect tank every 2-3 years.
Clean gutters and tank if necessary.
Disinfect tank using chlorine.
Slime on the inside of tanksMicrobial growthAll containers that continuously hold water will develop biofilms on surfaces below the water level.None required.None required. These are naturally occurring and not harmful to the general population.
White deposits on the surface of metal tanks (slimy or waxy feel)‘White rust’. A corrosion product containing zinc-rich oxide Not required.None required.None required, the deposits are not harmful. Physical removal could damage the surface of the tank and increase the potential for corrosion.