“Drinking water” – sometimes called potable water – is water that is safe for humans to drink and use for other domestic purposes, such as cooking, washing up, bathing and showering. In Australia, most water sources require some form of treatment to make them safe to drink.
According to the Australian Drinking Water Guidelines:
Ideally, drinking water should be clear, colourless, and well aerated, with no unpalatable taste or odour, and it should contain no suspended matter, harmful chemical substances, or pathogenic microorganisms.
In other words, drinking water should not contain chemicals, organic substances or organisms that can make us sick. Drinking water should also be at a reasonable temperature and free of odours, tastes and colour.
The guidelines also define drinking water as water ‘…which, on the current state of knowledge, is safe to drink over a lifetime: that is, it constitutes no significant risk to health’.
When most Australians turn on the tap, we expect a continuous supply of drinking water that meets these guidelines – water that is safe and pleasant to drink.
We expect it to flow at an acceptable pressure and to be available even in the middle of a drought. We also expect that our wastewater will not create a nuisance or public health hazard. Furthermore, we expect to be protected from localised or more substantial flooding. During the nineteenth century and particularly in the twentieth, engineers designed and built urban water systems to meet these expectations.
WATER AND PUBLIC HEALTH
The importance of good drinking water in maintaining human health was recognised long ago. Water storage and treatment are mentioned in historical records dating back nearly 3,000 years.
A pivotal step towards developing safe supplies of drinking water was the understanding that specific microorganisms cause specific human diseases.
In the mid-nineteenth century, London doctor John Snow linked water supplies to the spread of disease.
This was a major breakthrough. Dr Snow showed that cholera was not transmitted by ‘bad air’ or ‘filthy conditions’; rather, it spread through polluted drinking water, or contaminated food or objects. He was the first to use chlorine as a disinfectant for water.
By the early 1900s, rates of waterborne disease were greatly reduced in developed nations through better protection of water supplies from sewage pollution and simple but effective methods of water treatment, such as sand filtration.
The widespread introduction of disinfection in the early twentieth century improved public health even further.
However, waterborne diseases continue to be a major cause of illness and death in many parts of the world, where more than one billion people drink unsafe water. The World Health Organisation (WHO) estimates that each year 2.4 million deaths are caused by unsafe water and lack of sanitation.
Even in developed countries, contamination of drinking water still occurs occasionally.
In December 2007 in Nokia, Finland, drinking water was contaminated when sewage effluent entered the distribution system. Up to half of town’s 30,000 residents may have been exposed and more than a thousand cases of gastroenteritis are estimated to have been caused by the contamination. At least 250 people sought medical care and a number were diagnosed with Campylobacter and Salmonella infections.
‘BUGS’ IN THE WATER
Microorganisms that are capable of causing disease are called pathogens and include bacteria, viruses, and protozoa such as Cryptosporidium and Giardia. In water supplies, the pathogens of concern are mainly those found in faeces of humans or animals.
Pathogens of human origin are generally regarded as the greatest health risk from water supplies, as many of the significant water-borne diseases, such as cholera and typhoid, are found only in humans. If present in a water supply and not removed by treatment, these pathogens can cause infection in people who drink the water.
However, some pathogens carried by animals can also cause illness in humans. When such illnesses are water-borne, their most common source is mammals in water catchments (whether native, feral, or agricultural) and birds in service reservoirs.
Other microorganisms, called Blue-Green Algae, can grow naturally in our sources of drinking water. Some of these algae produce toxins or chemicals that can affect the taste and odour of the water.
To ensure that pathogens and algal toxins do not pose a health risk to the community, water supplies are treated in various ways before distribution.
A catchment is the entire area from which a stream or river receives its water. It is a natural drainage area, bounded by sloping ground, hills or mountains, from which water flows to a low point.
Most Australians live in a catchment, which may include hundreds of sub-catchments. What happens in each of the smaller catchments will affect the greater catchment.
Catchments are a crucial part of urban water systems, whether surface water or groundwater. The quality of the catchment determines the quality of the water that is supplied from it.
In a few highly protected areas, catchments exist in their natural state and minimal water treatment is needed. For example, most of the water supply for Melbourne and Canberra comes from natural wilderness catchments set aside solely for water collection.
Few communities, however, have pristine water sources and the quality of water from most sources is affected by conditions and activities in the catchment. For example, most of Adelaide’s water is derived from the Murray River, which has a vast catchment — the Murray Darling Basin — that is home to almost two million people and contains more than 50,000 farms.
Water is transported from catchments to communities in a variety of ways, including pipelines, aqueducts, open channels or natural waterways.
In some urban water systems, the water supply is obtained directly from a river or another body of fresh water. In others, rivers are dammed and the water supply is distributed from artificial storages, such as reservoirs.
Dams are built across rivers and streams to collect water from catchments in reservoirs, to ensure sufficient supply will be available when needed. Dams are also built for other purposes, such as irrigation and generating hydro-electricity.
In Australia, a large dam is defined as one with an
embankment more than five metres high. Australia has more than 400 large dams, and the largest of these is Tasmania’s Gordon Dam, which can hold 12,450,000 megalitres (one megalitre is one million litres).
Groundwater, from sources such as the Great Artesian Basin, is also a significant source of supply in many parts of rural Australia and for several major urban centres. Almost half of Perth’s water supply is groundwater.