04.Contaminants and additives
Tap water can contain many impurities, both natural and artificial. Some are harmless, or only affect what the water looks, tastes or smells like. Others can give you an immediate infection or slowly damage your health over a long period of time.
Some chemicals (such as chlorine and fluoride) are added to your water in the treatment plant. There are ongoing discussions over potential health risks as a result of this. But the benefits of using the chemicals are still thought to outweigh any potential risk.
Supplying water that's free from pathogenic micro-organisms (those that can make you sick) is the most important task for water authorities.
Bacteria: Most pathogenic bacteria found in water come from contamination by human or animal faeces. Disinfection (for example with chlorine) usually kills all bacteria. Another potential threat are bacteria growing in the water mains. That's why water suppliers try to ensure there's a residue of chlorine to protect the water on its way from the treatment plant to your home.
Protozoa: This group includes cryptosporidium and giardia. These can cause severe illness, and their cysts can often resist disinfection.
Viruses: Some viruses that can be found in water are potentially harmful. While disinfecting the water usually kills most viruses, some may survive and make you sick. However, it's not known how big a problem this is in Australia, as the source of a viral infection (whether it's water, food or contact with another infected person) is difficult to trace.
Pesticides and herbicides can leach into waterways in rural areas. Some are potentially carcinogenic and last in the environment for a long time. While low concentrations of these chemicals have sometimes been found, our drinking water is usually free of them when tested. However, not all water authorities check for them regularly.
Nitrate/nitrite: The main sources for these chemicals in waterways are sewage and fertiliser run-off. Groundwater supplies in rural areas are most likely to have high nitrate concentrations.
While nitrate itself is harmless, it can be converted into nitrite, which mainly poses a problem to babies and young children - it can reduce the amount of oxygen the blood can carry. In areas where nitrate is a problem, the water supplier will usually advise people to use bottled or rainwater for children under three months.
Chlorine and chlorination by-products: Chlorine or chloramine is usually added to kill bugs in the water that passes through the treatment plant, and to protect against recontamination while the water's travelling through the distribution system.
However, these chemicals can - depending on a number of parameters - react with naturally occurring organic substances in the water to form potentially harmful by-products (mainly so-called trihalomethanes, THM).
The drinking water guidelines state a maximum concentration for these by-products. They also point out that while their concentration should be minimised, the disinfection of drinking water must not be compromised. The risk posed by by-products is considerably smaller than that posed by the presence of pathogenic micro-organisms.
Fluoride has been added to drinking water since the 1960s and '70s as it has a proven record of reducing tooth decay.
However, fluoride protection is now available from more sources - for example, from many toothpastes or from fluoride treatments applied by your dentist. Critics say fluoridated water is unnecessary, as it may lead to dental fluorosis (mottled teeth) in people who get too much, and we don't know the potential health risk of drinking fluoridated water over a lifetime.
Aluminium: Chemicals containing aluminium are used in a process called flocculation, which removes suspended particles from the water, making it clearer. While most of the aluminium used can be filtered out of the water, small amounts may pass through. Some water authorities have phased out the use of aluminium chemicals in favour of alternatives.