Water used for household purposes such as drinking, food preparation or bathing should meet certain standards in order to protect you and your family's health. The water should be free of harmful micro-organisms or harmful levels of chemicals. By far the greatest potential risk to your health comes from contamination of water with harmful micro-organisms such as bacteria, viruses and parasites.
Of major importance is the protection of source water from contamination by human and animal faeces. Water may need to be treated to make it safe for human use. This may include removal of suspended material by settling or filtration, storage to allow organisms to die off, disinfection with chlorine or boiling or passage through a filter to remove a specific chemical contaminant.
The Australian Drinking Water Guidelines state: For an individual household supply, the emphasis should be on selecting the best quality source water available, and on protecting its quality by the use of barrier systems and maintenance programs. Whatever the source (ground, surface or rain water tanks), householders should assure themselves that the water is safe to drink. Information on the quality of surface and ground water may be available from state or local governments who may monitor the particular source water as part of a state or local water monitoring program. Alternatively, the individual should consider having the water tested for any key health characteristics identified as being of local concern. Where the raw water quality does not meet these guidelines, a point of use device (eg. filters) may be useful.
Rainwater Tanks
Rainwater from your roof can be a valuable resource particularly in areas where reticulated water is not available. To help ensure good quality water, it is important to correctly install and maintain the rainwater tank and catchment area.
What can go wrong?
Water collected from roofs may be tainted by substances washed off by the rain and may even be unhealthy to drink. These may be chemicals such as components of paint or wood fire deposits or they may be micro-organisms from bird and animal droppings. Contamination can also be caused by decaying leaves and dead animals which have fallen into the tank. In addition, tanks can act as breeding sites for mosquitoes which in some circumstances may be carriers of viral diseases.
Measures to Safeguard Tank Water Quality:
- Install screens on all tank inlets. Install first flush bypass devices which collect roof debris. These are available from tank suppliers.
- Roof gutters and screens should be regularly checked and kept clean.
- Cut back overhanging vegetation to prevent falling leaves, bird droppings and possum faeces from collecting on roof and in gutters. Bird and animal repelling devices could be considered.
- Keep wood heaters in good repair. Remove 'Chinese hat' type chimney flue cowls.
- Keep roof in good repair and check with suppliers of materials before using them on a roof used for collecting drinking water.
- To be assured of microbiologically safe drinking water, disinfect the tank with the appropriate amount of chlorine. If gross contamination occurs, such as finding a dead animal in the tank, empty and refill. In addition, in these cases the tank may need a higher dose of chlorine - seek advice. Until the tank is treated boil all water for drinking and food preparation.
Bore Water
Groundwater can be of high quality and suitable for human use, however shallow groundwater supplies can be prone to contamination. Potential sources of contamination include landfill sites, leaking underground fuel storage tanks, mining operations, septic tanks as well as sources likely to contaminate rivers and streams. As the water passes through the soil and rock it can accumulate chemicals which may affect its suitability for human use. Some of these substances while not harmful may adversely affect the taste of the water. To be certain that the source is suitable it may be advisable to have the water tested. Collecting a representative sample of groundwater requires a fair degree of planning and skill. In addition, interpretation of the results requires expertise in groundwater chemistry. Advice should be sought from Mineral Resources Tasmania which is responsible for groundwater in this state. In some instances it may be advisable to disinfect the water with chlorine before using. For more information about disinfecting water see Disinfection and Filtration.
Dam Water
Water taken from dams may need extra care because it is more difficult to prevent contamination from vegetation and animals. Native animals and feral animals as well as farm stock can pollute water courses and lead to contamination of dams. Dam water may be turbid after rain and need settling in tanks or clarifying before disinfecting with chlorine. For more information about disinfecting water see Disinfection and Filtration. Under certain conditions dams can be prone to algal blooms which may deposit toxins in the water. These chemicals may cause illness in people and stock consuming or bathing in the water. Boiling does not inactivate the toxins although activated carbon filters and chlorination may remove some toxins. Even if the water is used only for bathing and washing there are still limits for microbiological contamination which should not be exceeded.
Rivers and Streams
Surface waters, including rivers and streams, are subject to biological and chemical contamination which may come from stock access, native animals, septic tanks, dairies and piggeries and stormwater run off. It is possible for pesticides and fertilisers to wash off farm land and forestry operations and to contaminate water sources. As with other sources, microbiological contamination of the water is the most common cause of illness associated with consumption of water. Water can be tested for suitability, however advice should be sought regarding the number, timing and collection of water samples. 'One off' samples can be misleading. Clear running water is not always safe to drink. Where there is any doubt, the water should be boiled or disinfected with chlorine before household use. For more information about disinfecting water see Disinfection and Filtration.
Disinfection and Filtration
To disinfect water it is recommended that about 5 milligrams of chlorine per litre be used. This converts to 40 millilitres of sodium hypochlorite solution (12.5% chlorine) or 7 grams of calcium hypochlorite powder (75% chlorine) per 1000 litres of water. These chemicals are available from swimming pool shops and other suppliers. Other forms of chlorine such as stabilised chlorine should not be used. It is important that the chlorine is distributed throughout the tank for it to be fully effective. This can be achieved if the product is added while the tank is filling. Contact time for disinfection must be at least one hour. After this time the water should be safe to drink. A taste and smell of chlorine will be present but will disappear in a few days or sooner.
Small quantities of water needed for drinking can be effectively disinfected by boiling. Boiling clear water for one (1) minute on a rolling boil will kill bacteria, viruses and cysts. It should be noted that some electric jugs and kettles which cut out on reaching boiling may not be suitable for this purpose. If the water is very cloudy (turbid) it would be advisable for it to be kept on the boil for 3 minutes to eliminate all pathogens. Boiled water can then be stored in your refrigerator.
Filters (point of use devices) are available to remove a range of contaminants from water. Selection of the most appropriate will need careful consideration. All micro-organisms are only removed by certain filtration units so expert advice must be sought. It is essential that the units be well maintained as neglected filters may release bacteria and chemicals into the water in higher concentrations than the untreated water.