California reached a conservation milestone in September, when Gov. Arnold Schwarzenegger, R, signed a bill requiring all homes in the state to use water meters by 2025.

Existing California law requires water meters on all houses built since 1992, but most utilities charge a flat rate, rather than using the meters to charge by the gallon. Now, people will pay more if they use more, and utilities will have the ability to detect leaks and encourage customers to use their water wisely.

"Ornamental water meters are silly," says Ron Stork of the nonprofit group Friends of the River. "It’s time to get with the 20th century, now that we’re in the 21st."

Metering won’t be cheap, however. In Sacramento, the state capital, over 100,000 homes must be retrofitted; the cost, an estimated $300 million, will come out of the city’s pocket. Angela Anderson, a spokesperson for the Sacramento department of utilities, says the city objects to the metering mandate. Long-standing water rights guarantee the city enough water to meet present and future demands, she says, with or without such conservation measures.

Despite Sacramento’s complaints, it’s clear that charging people based on their water use works: Through metering and consumer conservation incentives, San Diego County has held its water use down. Residents used virtually the same amount of water in 2003 as in 1990 — despite a 16 percent population increase.