Urban water systems
The water cycle
Natural water cycle
In natural environments that have not been urbanised, much of the ground surface is permeable to water. Rain soaks in to the soil and recharges groundwater or slowly runs off into creeks, rivers and the coast once the soil has become saturated (fully wet). Water use by plants and animals is limited to what is available from the rainfall and natural flows.
Urban water cycle
In contrast to natural environments, the built-up areas in towns and cities have many hard surfaces that are impermeable to water (water runs off rather than soaking in). This includes roofs, roads and footpaths.
These impermeable areas reduce the rate that rain soaks into the soil and recharges groundwater. Larger volumes of water quickly run off these surfaces into the stormwater system (a network of drains) and then flow out to our rivers and coast. In many places what were natural waterways have been re-aligned (straightened) and concreted to help to drain this water away as quickly as possible in order to minimise the risk of flooding properties and roads that were built close to the waterways.
Depending on the soil type, rainfall pattern and amount of impervious area, urban developments will greatly increase the runoff compared to a natural area. These higher and more frequent runoff volumes and flow rates change the flow patterns in waterways and increase erosion of the creek bed and banks. This affects the plants and animals that live in our urban waterways and increases the flows discharging to the coast.
More water is needed to sustain urban populations than can be supplied naturally from local sources in South Australia’s hot and dry climate. Water is needed in our homes, businesses, schools and all activities.
Plus, the water requirements of many of our gardens, parks and playing fields is much higher than the natural ecosystems would have required. A complex water supply system delivers this additional water to our towns and cities.
Features of the urban water cycle
- Water is supplied from storages to treatment plants and to our taps through a network of pipes thousands of kilometres long.
- Wastewater from homes and businesses travels through a different network of sewerage pipes to treatment plants, where it is treated and then discharged to rivers or the coast – or reused.
- Stormwater pits and drains collect rainwater run-off from roads and roofs and carry it into nearby waterways or in some places, directly to our coastal waters. Some stormwater is captured and treated for reuse.
- Recycled wastewater and stormwater are used in some towns, cities and agricultural areas.
- Discharges to coast and rivers carry any stormwater or wastewater that can’t be used or stored for later use.
Urban water sources
Drinking water
SA Water is the largest water supplier in South Australia. Almost 99% of South Australians are supplied with potable drinking water by SA Water, which also supplies the water for most urban activities across the state.
The water supplied by SA Water comes from the River Murray, reservoirs in the Mount Lofty Ranges, groundwater and seawater that has been desalinated. In towns and cities this water is used for a wide range of indoor and outdoor activities, including drinking and washing; businesses and industries; and watering parks and playing fields.
Non-drinking water
Water that has not been treated to drinking water quality, known as non-potable water, is supplied in some places for uses such as watering gardens and parks and flushing toilets. This water supply comes from treated stormwater, recycled wastewater, groundwater and rainwater that runs off roofs.
There are many different non-drinking water suppliers in different parts of the state including local councils, SA Water and private suppliers. Some householders also capture and use rainwater from the roofs of their homes.
