A study by the Pacific Institute has found that seawater desalination is among the most expensive solutions to water scarcity in the state of California, US.

The average median cost of seawater desalination in large projects is $2,100 an acre-foot (1,233 m3), and for small projects is $2,800, the report states.

By comparison, large stormwater capture projects are among the least expensive, costing a median average of $590 an acre-foot.

The report uses a method borrowed from the energy industry to determine the ‘levelised cost’ of water. This accounts for the full capital and operating costs of a project or device over its useful life, and allows for a comparison of alternative projects with different scales of operations, investment and operating periods, or both.

Authors Heather Cooley, director of the water programme at the Pacific Institute, and Rapichan Phurisamban, research associate, found that brackish water desalination is much less expensive than seawater desalination owing to the lower energy and treatment costs involved.

Further, although non-potable reuse is cheaper than indirect potable reuse on the grounds of lower treatment requirements, the cost of building a separate distribution network to deliver non-potable water means that in fact indirect potable reuse may be a more cost-effective option overall.

Water conservation and efficiency measures were found to be the most cost-effective ways to meet current and future water demands.

The report, The Cost of Alternative Water Supply and Efficiency Options in California, evaluates the cost of stormwater capture, recycled water, brackish and seawater desalination, and a range of urban water conservation and efficiency measures.

The Pacific Institute is a global water think tank providing science-based thought leadership with active outreach to influence local, national, and international efforts in developing sustainable water policies.