Sea Water Desalination

City's plan to save water

JOHN YELD

Environment & Science Writer

THE CITY of Cape Town plans to call for tenders for a feasibility study on a large-scale seawater desalination plant, as the region runs increasingly close to using all of its available fresh water supply.

The tender call, expected within a month, will be for a study on where such a desalination plant could be built and what capacity it should have.

The call coincides with a major effort to plug water leaks and theft that, in February last year, accounted for one quarter of all treated water in the city, and with a warning that few options remain for tapping existing surface water sources.

The city will also be looking at the large-scale re-use of water. This is the only potential major new water source at a cost lower than seawater desalination, which is very expensive because of the large amount of electricity required. This study is expected to kick off “within the next few months”.

These initiatives are among the water conservation and water demand management measures that form a major part of the strategy for providing water in the Western Cape region that is already using about 92 percent of all “safely” available water. “Safely” means with a high degree of certainty of availability, without water restrictions.

Depending on how successful these measures are and on how much the city grows, the remaining 8 percent of available water will be fully utilised anywhere between 2017 and 2019, according to projections by the Department of Water Affairs.

In a statement yesterday based on the latest newsletter of the Western Cape Water Resource Strategy’s steering committee, the department said it was therefore supporting the city’s efforts by calling on all residents to use water sparingly.

It pointed out that the Western Cape Water Supply System could safely provide 556 million cubic metres a year. Users of this system include the municipalities of Stellenbosch, Drakenstein, Swartland and Saldanha, as well as farms.

Last year, 511 million cubic metres were used, with 32 percent going to irrigation farmers and 68 percent to urban residents.

The department pointed out that the city had invested some R60m in the current financial year to upgrade and replace water infrastructure, metering, water pressure management and other measures to reduce water loss and the amount of “non-revenue” water.

Cape Town action on desalination and water reuse

The City of Cape Town, South Africa, is planning to issue a tender for a feasibility study of a "large‐ scale" seawater desalination plant within the next month. The study will determine the most appropriate location and size for such a plant.

In addition, the City also plans to do a feasibility study into the large‐scale reuse of water, the only remaining major potential source of augmenting the area's water supplies at a lower cost than desalination, due to the smaller electricity requirements. This study will also commence within the next few months.

Investigations by the city into the potential for large‐scale ground water development and utilising the Table Mountain Group (TMG) aquifer as a sustainable water resource are also underway. A decision on the implementation of a pilot wellfield development in the TMG will be taken by the city in the next couple of months.

These actions follow the release of the latest Western Cape Water Supply System Reconciliation Strategy covering the period October 2010-March 2011. According to the study, only a few surface water development options are available for augmenting water supply to Cape Town and surrounding towns.

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