Probably no statement about South Australia has been given wider currency that its claim to be the driest State in the driest continent. Only 3.3% of the land area receives a mean annual rainfall above 500 mm, while about 83% receives less than 250 mm. There is very little runoff within the State and the most important source of supply is the River Murray, which originates from head-water sources outside the State. The scarcity of water has made it necessary to develop resources that would be considered marginal in better-endowed regions; economic life in South Australia has depended to an unusually high degree on water transported over long distances in pipelines.
The presence of water flowing in the River Torrens was an important factor in Colonel Light's choice of the Adelaide Plains as the site for the capital. For the first twenty-four years the population of Adelaide was supplied with water from the Torrens and nearby streams by horse-drawn water carts. This system proved inadequate, especially in summer, and in 1860 the first reservoir was constructed at Thorndon Park to hold water diverted from the Torrens. Piped water was first supplied to some streets in Adelaide on 28 December 1860 at a price of only 6% of the rate charted by the water carters. Until the mains were extended to Port Adelaide, water was carted there in railway tankers. Hope Valley Reservoir, built in 18722, held further storage from the River Torrens. In 1892-96 development of the Onkaparinga River resources began with construction of Happy Valley Reservoir to which water was supplied through a 5 kilometre long tunnel from a diversion weir at Clarendon.
Water supplies in rural areas were at first confined to semi-permanent streams, soaks or springs, and wells and small earthen dams. The development of a reliable reticulated water supplies was a consistent objective of government policy from the 1890s. A wide area between Port Augusta and northern Yorke Peninsula was serviced from an interconnected system of pipes from three reservoirs constructed at Beetaloo (1890), Bundaleer (1902) and Baroota (1920). The Barossa Reservoir built in 1902 and fed by the South Para River, at first supplied Gawler and adjacent country areas, but since 1945 it has also been linked with the metropolitan system.
On Eyre Peninsula only one stream, the Tod River, can be relied upon to provide some flow in most years. The Tod River Reservoir was completed in 1922 and serves an extensive pipeline system from Port Lincoln to Ceduna.
By 1940, it was apparent that most of the sites at which surface runoff could be economically held in reservoirs had been developed, and that the River Murray would be the most important water source in the future. The first pipeline from the Murray was constructed from Morgan to Whyalla between 1940 and 1944 to supply the new industrial town of Whyalla, and to supplement existing northern reservoirs. This pipeline was duplicated in 1962.
The construction of barrages prevented seawater entering the Murray Mouth and made it feasible to supply Adelaide with water from the river. The pipleline from Mannum to Adelaide came into operation in 1954; it discharges into the River Torrens system of reservoirs - Hope Valley, Millbrook and Kangaroo Creek - and into the Little Para Reservoir. The second metropolitan pipleline, from Murray Bridge to the Onkaparinga River near Hahndorf, was completed in 1973. Three pumping stations lift the water up 418 metres over the first 40 kilometres of the 48 kilometre pipleline. This flow supplements the natural inflow into the Mount Bold Reservoir. Since their completion, the two pipelines have supplied about 40% of metropolitan Adelaide's water consumption, with an increased amount in dry years.
The quality of Adelaide's water has long been the butt of unfavourable comments because turbidity, taste and odour are often at levels considered unacceptable in urban supply. The first of six proposed filtration plants to improve water quality was opened at Hope Valley in 1977, followed by plants at Anstey Hill, Barossa and Little Para. Plants at Happy Valley and Myponga will complete the programme.
Two further pipelines were constructed in the 1960s to supply country areas with River Murray water. The Swan Reach-Stockwell pipeline connects with the system serving Yorke Peninsula and the Tailem Bend-Keith pipeline serves the Coonalpyn Downs area.
Approximately 90% of the population of South Australia is now wholly or partly dependent on reticulated water from the River Murray. Of the urban and rural water-supplies controlled by the Engineering and Water Supply Department (E&WS), the share of the total intake derived from the Murray has varied from 85% in drought years to less than 30% in years of above-average rainfall.
The River Murray is also by far the major source of irrigation water in South Australia. Annual diversions for irrigation purposes from the river typically amount to almost twice the quantity of water drawn from the urban and rural reticulation systems of the E&WS. In 1984-85, the State's total estimated water consumption was 751,000 mega-litres. River Murray irrigation areas, government and private, accounted for 56% of the total, E&WS reticulated systems for 34%, and underground withdrawals in three proclaimed irrigation areas - the Northern Adelaide Plains, Padthaway and Angas Bremer - for 9%.
Many areas of the State depend on underground water sources, particularly for watering livestock, and some areas rely at least partly on underground water for their reticulated supplies. The total number of flowing or pumping wells in South Australia is estimated to be about 150,000. Towns in the South-East rely entirely on flow from natural springs and shallow underground basins, and most town supplies on Eyre Peninsula come from underground basins.
The Great Artesian Basin which extends into the northeastern quarter of the State has been vitally important to its pastoral occupation and is of growing significance to its mining activities. The salinity level of groundwater over much of the rest of the State is too high for domestic use, and for about half the areas of the State it is also too high for most livestock.