URBAN WATER SYSTEMS

When most Australians turn on the tap, they expect a continuous supply of safe and pleasant drinking water. They expect it to flow at an acceptable pressure and to be available even in the middle of a drought. They also expect their wastewater will not create a nuisance or public health hazard. Furthermore, they expect to be protected from localised or more substantial flooding.

During the 19th and particularly the 20th centuries, engineers have designed and built urban water systems to meet these expectations.

Following is a brief overview of the main components of an urban water system.

The entire area from which a stream or river receives its water is called a catchment. A catchment is a natural drainage area, bounded by sloping ground, hills or mountains, from which water flows to a low point.

Virtually everybody lives in a catchment, which may include hundreds of sub-catchments. What happens in each of the smaller catchments will affect the main catchment.

The water that comes out of a tap once flowed across a catchment - and that is why catchments are a crucial part of urban water systems.

The quality of the catchment determines the quality of the water harvested from it. Few communities have pristine water sources and the quality of water from most sources is at risk from activities occurring in the catchment.

Water resources can be classified as surface water or groundwater resources. In both cases the quality of the catchment determines the quality of the water harvested.

Groundwater is a significant source of supply in many parts of rural Australia. It is also a significant ongoing source for several major urban centres. In 1998/99, the water supply for Perth, Western Australia was 47 per cent groundwater, and that of Newcastle, New South Wales was 24.5 per cent groundwater. Also the regional water authority supplying Geelong, Victoria and areas to its west used 33.2 per cent groundwater in 1998/99 as drought impacted on its surface water sources.

In parts of inland Australia, water from the Great Artesian Basin is used for urban, agricultural and mining purposes. This water source is of vital importance to outback regions of Queensland, New South Wales and South Australia and is often the only available supply for towns and properties for their domestic and stock-watering requirements.

In some urban water systems, the water supply is obtained directly from a river or another body of freshwater. 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 create reservoirs to collect water from catchments to ensure sufficient supply will be available when needed. Dams also have been built for a range of purposes besides water supply, such as agriculture and hydro-electricity generation.

Water may also be released from a reservoir as an "environmental flow" to maintain the health of the ecosystem downstream of the reservoir.

It is estimated that the significant reservoirs built around the world store five billion megalitres of water.

In Australia, more than 400 water storages are technically defined as "large dams". A large dam is defined by the Australian National Committee on Large Dams (ANCOLD) as one that has an embankment more than five metres high. There are also innumerable smaller water storages.

Australia's largest reservoirs

Water is transported from catchments to communities by a variety of means including pipelines, aqueducts, open channels or via natural waterways.

Water that is to be used in an urban supply is treated to remove sediments and contaminants and is also disinfected to kill potentially harmful microorganisms. The treatment process may use conventional technologies or apply newer, innovative approaches, to ensure the water is safe and pleasant to drink.

The water mains and pipes beneath the streets of a community are described as the water supply distribution system or reticulation system. As part of this system, strategically located service reservoirs store and supply enough water to meet local peak demand at sufficient pressure. These service reservoirs are often large covered tanks in an elevated position.

Pumps and valves also form an important part of the distribution system. The end points of the system are the consumers’ taps.

Urban wastewater is known as sewage, and the pipes that transport sewage are called the sewerage system.

No matter where you use water inside your home - the kitchen, bathroom, laundry or toilet - it is discharged to the sewer. From there, your wastewater begins a journey through a series of sewer pipes, pumps and mains to a sewage treatment plant.

Wastewater from industry, schools, shops and other sources is also discharged to the sewerage system.

At sewage treatment plants, wastewater is treated in a way that mimics natural biodegradation processes. After intense treatment, the treated wastewater is discharged back into the environment. Wastewater is treated to protect public health and to minimize impacts on the ecosystems of receiving waters.

Treated wastewater is increasingly being recycled or reused in agriculture, horticulture, golf courses and other businesses. A number of innovative housing developments are using dual water supply systems where recycled wastewater is supplied for some domestic purposes such as garden watering and toilet flushing, while conventional drinking water is supplied for other household uses.

Water recycling

Where homes and businesses are not connected to a sewage system, they will usually have some form of on-site treatment of sewage. Such on-site treatment needs to include provision for the safe discharge of the treated sewage into the local environment to protect both public health and local ecosystems. The septic tank is a common form of domestic on-site treatment.

Stormwater is the term used to describe the runoff from rain over an urban catchment. In cities and towns, stormwater washes across roads and streets, picking up oil, petrol, grease, sediment, industrial waste, leaf and other litter and dog droppings on roads, streets and paths.

In rural areas, runoff may include agricultural and livestock waste, fertilisers and pesticides.

Stormwater can also be contaminated by landfill leachate, septic tank effluent, sewer spills and by illegal dumping. It is estimated that contaminated stormwater causes up to half the pollution in surface and groundwater sources.

Most major urban centres now use separation systems, litter traps, grates, retention basins or boom barriers to reduce the quantity of larger objects carried in stormwater before it is discharged to the environment.