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Description of hazards and hazardous events

By providing clarity with regard to what constitutes a hazard and hazardous event in the context of a facility plumbing system, this information sheet should assist the risk assessment process, and support the development of appropriate control measures for those hazards and hazardous events.


The hazards that must be controlled in a facility’s water distribution system may arise from within the water distribution system or from outside. These hazards may be microbial, chemical or physical.

Microbial hazards

A pathogen is any bacterium, virus, protozoan or other microorganism that can cause disease in people. The water risk management plan (WRMP) for a hospital or residential aged care facility must consider all pathogens that can be transmitted in the water used by the facility. There are two kinds of water-borne pathogens: enteric and environmental.

Enteric pathogens

Live in animal intestines and are normally transmitted via the faecal-oral route:

  • Some enteric pathogens are present in drinking water sources, particularly dams and rivers, and may originate from either animal or human sources.
  • Your drinking water service provider monitors for the risk of enteric pathogens, and generally treats the water via filtration and disinfection to remove pathogens.
  • Once water has been received by a facility, it may still become contaminated with enteric pathogens through the ingress of untreated water to cracked or damaged drinking water pipes, failure of backflow prevention devices from washing machines, pan washing facilities, or cross-connection with non-treated water such as roof-harvested water.
  • Enteric pathogens include Cryptosporidium, Giardia, Enterovirus, Adenovirus, Campylobacter, Salmonella, and pathogenicforms of Escherichia coli (E. coli).

Environmental pathogens

Commonly found in both natural and artificial water sources:

  • Some are successful at surviving water treatment processes, including disinfection and may therefore occur in the treated potable water supply received by a facility.
  • These pathogens have the ability to colonise and grow in the water distribution systems of buildings.
  • Environmental pathogens that can be water-borne include Legionella, nontuberculous mycobacteria (NTM) and Pseudomonas aeruginosa.

Environmental pathogens are more likely to colonise the water distribution system of a facility under certain conditions, such as, but not limited to:

  • the presence of a biofilm which provides shelter and nutrients
  • use of inappropriate water filters,  for example carbon filters, which not only remove chlorine but can also provide a suitable environment in which bacteria may grow.
  • increased organic matter in the water provides food and protects the pathogens from disinfection
  • areas of low flow or stagnant water, such as dead legs and disused taps
  • no or low disinfection residual in the water.

Surrogate and indicator pathogens

It would be an expensive and time-consuming exercise to test for all potential pathogens in facility water supplies, particularly when most pathogens will be absent most of the time. Water managers therefore typically choose a microbial indicator which, if not detected, gives some reassurance that the control processes intended to remove pathogens is effective.

In Queensland, drinking water service providers test their treated water using E. coli as the indicator organism for enteric pathogens.

Drinking water service providers may test for additional pathogens, like Cryptosporidium, if they have identified a specific risk from their catchment or source water.

The most useful indicator for environmental pathogens in plumbing systems is Legionella. Control measures implemented for Legionella will, to some extent, also control non-tuberculous mycobacteria (NTM) and Pseudomonas, although it should be noted that NTM are more resistant to disinfection than Legionella.

Chemical hazards

The water supplied by a registered drinking water service provider is required to comply with the Australian Drinking Water Guidelines. Generally, this will ensure the water is free from chemical contamination at the point where it enters the facility.

Depending on the equipment you use in your facility, there may be times when the incoming water, although it may meet those guidelines, may still be a problem.

For example, manganese and iron may cause problems associated with taste, odour and colour at low concentrations. At concentrations at which they become visible, manganese and iron can cause staining of clothes and linen during washing, and can be deposited in pipes leading to scaling. In some parts of Queensland, there are persistent problems associated with iron and manganese.

Other chemicals that you may wish to discuss with your drinking water service provider, particularly if you have dialysis units, are aluminium and trihalomethanes.

Elevated water hardness can also promote scaling within pipes and elevated electrical conductivity can also affect dialysis machines.

Chemical contamination can also occur after the water has entered the facility. Metals, such as copper, lead, nickel and cadmium can leach from pipes and plumbing fittings.

Some chemicals can also leach from flexible hoses and plastic fittings, particularly when highly alkaline flushing is used to sanitise pipes.

Low pH leaches heavy metals and at high pH chlorine is less effective.

Back siphonage of disinfectants, anti-scalants and coolants can occur from equipment such as chlorinators or boilers.

Pesticides and fuel oils can also leach from soil into buried PVC pipes.

Physical hazards


Turbidity is the cloudiness or haziness of water, caused by large numbers of individual particles, which individually are too small to be seen with the naked eye. Silt, microorganisms, organic matter and chemicals contribute to the turbidity of the water.  In turbid water, microorganisms can be shielded from disinfection. Taste and odour problems may also be associated with turbid water. The particles that make the water turbid can also cause abrasion and wear on plumbing, stain sinks and fixtures and result in staining of laundered fabrics.


Cold water temperature above 20°C can support growth of biofilm and biofilm associated bacteria. Hot water temperatures above 43°C can also give rise to scalding risks.

Hazardous events

A boil water alert

May be issued by a drinking water service provider when there has been a detection of E. coli in the water supply, or when the disinfection process at the water treatment plant has failed. Your facility should be aware of the method your drinking water service provider uses to issue boil water alerts or any other responses to water quality issues. These methods may include door to door contact, leaflet drops or other community announcements.

Interruptions to supply

These can occur when your drinking water service provider undertakes routine maintenance on their infrastructure, or when an accidental pipe breakage occurs. In addition to managing the time when no water is being delivered to the facility, the WRMP should outline the steps to ensure the water supply in the facility is safe once the water connection is restored.

Interruptions to supply and poor quality water can also occur when construction of nearby facilities/building is taking place or during disasters such as floods, cyclones and bush fires. In disaster situations, the disruption could continue for an extended period.

Equipment failure

Interruptions to the supply of safe water within a facility can also arise from failure of equipment such as chlorinators, circulation pumps and thermostatic mixing valves. The facility should be aware of the risk to water quality from these events and ensure appropriate corrective actions have been included in the WRMP.

Last updated: 27 January 2017