Any water supply which is not a Town mains which meets drinking water standards should be considered a possible source of microbiological contamination. These can include bacteria like E.coli, Salmonella and Campylobacter. Viruses like Hepatitis A & E, Norovirus and Calcivirus. As well as Protozoan parasites like Giardia.
As these are living organisms, they are likely to be present intermittently and the number of them present will vary.
These are commonly found in rain water supplies, a surface waters, springs and shallow or unsecured bores. This can also be a concern with some water schemes, particularly irrigation schemes that some people have connected to their homes.

Chemically rain water is very good, however as it falls through the air, it dissolves in some Carbon Dioxide, which makes it slightly acidic and corrosive to metal plumbing. This is more noticeable in plastic tanks, concrete tanks can offer some protection as they raise pH slightly.

Bore/Well/Spring Water
There are a good number of people on these supplies supply in the region, these often have undesirable levels of iron, manganese, hardness, Silica and low pH
Those near the coast can have additional issues with salty water intrusion.

Surface Water (Streams, Rivers, Creeks Dams etc)
Surface water sources are not common in this area. Those which are present tend to have heavy levels of sediment in them after rains and they can become discoloured from dissolved organic matter. Depending on the land they flow through, some can also have other mineral issues, like hardness and iron.

Water Schemes
Occasional a small community may create their own water scheme to provide water to a number of houses in an area without a town supply. Some of these may leave the responsibility for drinking water safety in the hands of the home owner who has elected to connect to the scheme. These need to be tested and depending on the water source may experience some of the water issues described above.