Perth's water supply

Perth, the capital city of Western Australia, has a different water supply from that of any other Australian capital city. It is the only one where groundwater (water from beneath the earth's surface) is used for the public drinking-water supply. Unfortunately, there has been an increasing reliance on groundwater for other purposes, because above-ground sources are not coping with the demands placed upon them.

The Perth metropolitan region receives its water from the Integrated Water Supply System (IWSS). This system services all homes within the area from Quinns Rocks (in the northern metropolitan area (Heinemann Atlas 3^rd edn, page 42, map reference B3) to Mandurah in the south (map reference B1).

A further component of the IWSS is the Goldfields and Agricultural Water Supply (GAWS). Via this system, water stored in reservoirs close to Perth is transported through an ingenious system of pumps and pipes to the agricultural and gold mining areas lying to the east of Perth. This system stretches eastwards from the reservoir of Mundaring Weir in the Darling Ranges to Kalgoorlie, a distance of more than 590 kilometres.

A history of squandering water

Unfortunately, the lifestyle of people living in Perth has been one of extensive and relatively unchecked water use. Nearly 50 per cent of all the water used in metropolitan Perth is used on gardens. And it is no surprise – Perth gardens generally feature luxurious, non-native water loving plants, and the city is characterised by its sprawling parks and reserves with lush green lawns and open spaces. The people of Perth, like most Australian urban dwellers, have shown little interest in reusing household water, installing rainwater tanks or switching to ‘water wise’ gardens that make use of plants that cope well in dry summer conditions – all techniques that help to reduce the overall level of water use.

Struggling water supply

Now, in the face of an increasing urban population, the lifestyle of Perth homeowners means the IWSS that services their homes is struggling to cope. Domestic water use has increased 20 per cent per capita in the last 20 years. The population of Perth continues to grow at 1.7 per cent annually, placing additional pressure on the water supply system.

Climate change makes things worse

Perth normally has mild, wet winters (see the rainfall graph on page 40 of the Heinemann Atlas 3^rd edn). Winter rain should help fill the city's above-ground reservoirs. However, for approximately the last 25 years, Perth has been experiencing drier than average winters. This has reduced the amount of surface flow into Perth’s above-ground reservoirs, In turn, this has placed a heavy reliance on below-ground sources of water, those used for the public drinking-water supply. Groundwater is used for this purpose because there is just no other viable option at present.

Perth's decreasing rainfall pattern

Recent estimates by the Australian Academy of Technological Sciences and Engineering have pointed to a natural phenomenon causing a decrease in Perth’s annual rainfall. At this stage, this particular phenomenon is not completely understood. It could either be a small switch in the rainfall pattern, as has been experienced at various times in the past, or an indicator of longer term climatic change due to global warming. Regardless, the latest estimates by the CSIRO point to the current pattern of lower annual rainfall continuing in the southwest corner of Western Australia for the next 70 years. This causes a major problem for the IWSS, with half of its annual supply normally coming from above-ground reservoirs.

Coming water shortages

As a result of lower rainfall, it is expected that Perth will face a water deficit within the next 15 years. Massive lifestyle changes are needed – people will need to change the way they use water. The State Government, through its service provider the Water Corporation, has begun to establish these changes.

Water restrictions instituted

During the summer of 2001/2002, restrictions were applied to water users in metropolitan Perth in an effort to ensure that supplies could be guaranteed through the summer months. The Water Corporation has also embarked on a massive education and advertising campaign in an endeavour to raise public awareness about the need to be ‘water wise’.

Old habits die hard: other options

Changing the habits of an urban population is a long and difficult process. It may take many years. Other options to augment supplies within the system and to help guarantee the long-term future of the IWSS are now being considered. Among these options, the most viable would appear to be:

• utilisation of new sources of groundwater trapped below the surface of south-west Western Australia
• development of a desalination plant to service metropolitan Perth
• piping water to Perth from tropical areas of northern Australia that experience high levels of summer rainfall.

In this Atlas Update, you will consider the current nature of the IWSS and evaluate the merit of each of these three options that are planned to ensure its long-term viability.