Private water supplies are those sources of water not provided by a public water supply authority. In many rural areas they are the only source of water and are usually derived from rainwater harvesting, creeks, or bores. Even in relatively pristine areas, it is possible for such water supplies to become contaminated.

Sources of Contamination

Your private water supply can be contaminated by things such as:

• Animal faeces - bird or possum droppings on the roof, or from farm run-off into rivers and creeks.
• Human faeces- leaking from septic systems or wastewater drainage.
• Pesticides and herbicides - runoff from farms, or blown onto roofs.
• Fertilisers – runoff from farms, drift from spraying
• Arsenic and heavy metals- in soil from old industrial or mining sites, or in some bore water supplies.
• Dust- containing chemicals may be blown onto your roof.
• Air pollution – rain falling through polluted air absorbs chemicals; also air pollution deposits chemicals on roofs which is then absorbed in the runoff
• Lead - from old paint or flashing on roofs can flake and end up in tanks.
• Algae - including toxic blue-green algae which is not destroyed by boiling or disinfection.
• Nitrates - in some bore water supplies are particularly dangerous to infants.
• Ash and debris – bushfires produce large amounts of smoke and ash, which can contaminate your water supply.
• Fire retardants – chemicals used to slow the spread of fire can contaminate water with ammonia and sulphate, making it unsuitable for humans and animals to drink

Gastric Illnesses

Giardia and Cryptosporidium are commonly transmitted via animal and human faeces. These organisms in contaminated water supplies have been responsible for major outbreaks of severe gastric illnesses such as gastroenteritis and infections. These illnesses are particularly dangerous to the very young, the elderly, and people with poor immune systems.

Cryptosporidium are particularly resistant to chlorination and are difficult to detect and remove from water supplies.

This is of even greater concern during doughts as the dry periods allow a greater build up of dust and droppings in roofs and gutters. When the rain arrives, the falls are often sudden and heavy, washing this debris into tanks and resulting in above average contamination of water, particularly in tanks without a first flush diversion device.

First Flush Devices

In fact, even where first flush devices are fitted there has been some question as to whether they work as well as they should - see, for example, Rainwater First Flush Devices – Are They Effective? ¹ In this report the authors concluded that
"...in terms of microbiological quality, diversion of the first flush will not provide rainwater in compliance with the ADWG [Australian Drinking Water Guidelines], even though discarding the first 1 mm will reduce the load of bacteria entering the tank...",
"...in highly urbanized areas, particulate concentrations of Pb [lead] and Zn [zinc] were often above potable water standards even after the first 1 mm runoff..." and
"...some form of disinfection should be applied to tank water if used inside the home (other than for toilet flushing)..."

Footnotes

1 Rainwater First Flush Devices – Are They Effective? Gardner T, Baisden J and Millar G (2004) 'Sustainable Water in the Urban Environment, 2004 Conference', Brisbane, Australia. August 30-31, 2004.