Because desalination is not economically feasible, the water is more expensive and this extra subsidy raises the cost of the water bill.

This is how it works for the facility in San Diego County.

Building a desalination facility is economically hard to justify because the break-even point seems far away. It also assumes the state won’t eventually create a state-wide solution, which would benefit from a state-level economy of scale that a city/county effort might not.