* S.Africa turns to oceans for drinking water
*Sees more desalination plants in coastal towns
CAPE TOWN, April 15 (Reuters) - South Africa will increasingly use desalinated seawater to meet growing demand for drinking water in coastal towns facing the worst drought in 150 years, the country’s water minister said on Thursday. South Africa is a water-scarce country with an average rainfall of 450 millimetres -- compared to a world average of 860 mm -- and conditions are expected to worsen as a result of global climate warming.
"South Africa has a boundary consisting of approximately 3,000 kilometres of sea water, and this water is presently unusable because of its high salt content," Water Affairs Minister Buyelwa Sonjica said in her budget vote speech on Thursday.
"We therefore made a decision to press ahead with unconventional water treatment, in this case desalination, largely because of the unavailability of river water due to drought," she said.
Popular tourist coastal towns Plettenberg Bay, Knysna, George and Mossel Bay are facing severe water shortages due to prolonged drought in the southern Cape region.
These towns have turned to purifying seawater, as well as treating so-called grey water -- waste water generated from domestic activities like laundry and bathing -- to help meet their drinking needs.
Cape Town is also eyeing the option of desalinating water.
"Desalination has become the preferred purification option in terms of both the cost benefit and the flexibility of application," Sonjica said.
However, she said the government needed to exercise caution in extending its desalination programme because of possible negative effects to the environment.
"There is ample scientific evidence that the impact of the effluents from the desalination plants on the seawater environment increase the seawater temperature, salinity, water current and turbidity," said Sonjica.
Desalination is big business in the desert conditions of some Middle East countries, where it is a major supplier of clean drinking water to economic hubs such as Dubai. (Reporting by Wendell Roelf; Editing by Elizabeth Fullerton)