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.