Public Drinking Water
Drinking water is treated to protect public health by removing micro-organisms and natural or man-made chemicals that may cause illness in consumers. Water treatment may also be used to improve the water's colour, taste and odour as required.
Protection of water sources from pollution by human or animal waste can reduce the amount of micro-organisms entering the water supply, but even water from the most pristine environment may sometimes contain micro-organisms capable of causing human disease. Illness can be easily and rapidly transmitted to large numbers of people by contaminated water supplies, therefore it is necessary to treat and disinfect water supplies to safeguard against disease.
Innovative water treatment technologies are being developed in Australia and overseas with the aim of improving water quality further and reducing the cost of doing so.
Microorganisms that are capable of causing disease are called pathogens. The pathogens of concern in water supplies are mainly those that are found in the excrement (faeces) of humans or animals. If these microorganisms are present in water, and are not removed by water treatment or disinfection, then consumers may suffer infections.
Many types of pathogenic bacteria, viruses, protozoa and Helminths may be transmitted by contaminated water supplies. Generally, faecal contamination from human sources is regarded as the greatest risk to water supplies. However, some pathogens from animals including mammals and birds can also cause illness in humans.
Waterborne Diseases - Pathogens
Bacteria are tiny, single-celled microorganisms that are often observed forming colonies. They can occur in various shapes, for example, round, rod-like, or spirals. Typically, they can be as small as half to one micron wide, and as large as several microns long. Bacteria capable of causing human illness through contaminated water supplies include Campylobacter, Salmonella, Shigella, Vibrio and Yersinia. Other bacteria of environmental origin may be found in water supplies including Aeromonas, Legionella, Mycobacterium and Pseudomonas aeruginosa. If found in drinking water, these bacteria are generally less of a health risk than those of faecal origin.
Viruses are a large group of infectious agents, much smaller than bacteria, and are able to be viewed only through an electron microscope. They are not cells but biologically active particles that vary in size from 0.01 to 0.1 microns. Viruses may survive in the environment for some time in soil or water, but they cannot multiply unless they infect a suitable host. The viruses that are of concern for water supplies can only infect humans, therefore they can arise only from human waste. Viruses cannot be simply cultured in the laboratory in the way bacteria are identified, and for this reason it is difficult to detect viruses. Problem viruses identified in the Australian Drinking Water Guidelines include adenovirus, enterovirus, hepatitis viruses, norwalk viruses and rotaviruses.
The term protozoa refers to a collection of generally colourless, single-celled organisms with a well-defined nucleus. They are much bigger than bacteria, ranging in length from 5 to 100 microns. Protozoa are among the simplest of all living organisms. As a group, protozoa are extremely diverse. Pathogenic protozoa found in water supplies include Cryptosporidium, Giardia, Cyclospora, Naegleria, Acanthamoeba and Entamoeba.
Other causes of waterborne disease in humans include helminths. These worms or worm-like parasites infect the intestine and include roundworms, tapeworms and flatworms. The worms in humans that originate from helminth eggs are relatively easy to cure and present a problem only in developing countries where proper nourishment is a problem.
Disinfection of water, using treatment methods such as chlorination, has removed the threat of waterborne epidemics and reduced infant mortality rates to very low levels in Australia. Without disinfection, Australians would still be at risk from diseases such as cholera.
However, there is a downside to disinfection; the use of oxidants for disinfection, taste, odour and colour removal can produce undesirable organic byproducts. During chlorination of water supplies, the chlorine reacts not only with the microorganisms but also with most of the other organic material present in the water, either dissolved or in suspension. This produces a range of organic compounds known as disinfection byproducts.
These disinfection byproducts contain halogens, a group of elements with similar chemical properties. These halogens are fluorine, chlorine, bromine and iodine. While a lot remains to be known about many of these disinfection byproducts, they include a group of chemicals called trihalomethanes (THMs), mainly chloroform (trichloromethane), plus a broad range of other compounds.
Several epidemiological studies have indicated a possible association between chlorinated drinking water and increased risks from a variety of cancers, mainly to do with the bladder, colon and rectum. However, other studies have not found such associations. Therefore, because of the limitations of the data, no definite conclusions can be based on these studies.
Australian Drinking Water Guidelines
Development of drinking water guidelines in Australia
Australian drinking water guidelines, first issued in 1972 are designed to follow the World Health Organization recommendations modified for Australian conditions. In 1996, Australian Drinking Water Guidelines was published jointly by the National Health and Medical Research Council (NHMRC) and the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ). The Guidelines were reviewed and updated again in 2004 and published by the National Health and Medical Research Council in collaboration with the Natural Resource Management Ministerial Council (formerly ARMCANZ).
These guidelines are subject to review by these organisations and are updated as new medical and scientific information becomes available.
The document provides guidance to the Australian water industry on the treatment levels and procedures needed to manage water supply systems that are required to produce safe and pleasant drinking water.
Download a copy of the Australian Drinking Water Guidelines here;