Looking into a crystal ball a decade ago, San Diego water officials expected dramatically rising demand for water. The region would be using 242 billion gallons of water a year by 2015, they thought.

They were wrong.

In reality, the recession hit and growth stalled. Droughts came and Californians learned to save water. San Diegans are using far less water than expected – just 176 billion gallons last year.

Demand will remain flat for the next five years and then grow only gradually, according to a draft of the San Diego County Water Authority’s latest long-term plan.

These Urban Water Management Plans must be updated every five years. They help determine if there’s enough water for new development and help decide which multimillion-dollar water projects customers will be asked to pay for next.

Inaccurate projections are costly. If water officials underestimate water needs, we’ll be rationing water. If water officials overestimate demand, we’re left paying for expensive projects that aren’t needed.

In 2007, the region’s demand hit a record level just before the recession: 241 billion gallons. Demand is now expected to remain below that for the next 25 years, according to the Water Authority’s new projections.

Since the 2007 peak, demand has fallen by more than a quarter, something that began happening even before Gov. Jerry Brown last year ordered California’s urban water customers to cut their use by 25 percent. The governor got rid of those emergency cuts this week, but left in place some water-use restrictions and said he expected Californians to keep saving water.

The Water Authority now expects San Diego customers will indeed keep saving water. That’s one reason previous projections don’t match the current reality – officials didn’t expect customers to save so much water.

Water officials also were led astray by overly ambitious population and housing projections made by the San Diego Association of Governments. The Water Authority relies in part on those projections, though since 1990, SANDAG has consistently predicted far more growth than we’ve actually experienced and did not initially appreciate how many people would live in apartments rather than water-hungry homes.

Of course, lower demand doesn’t mean lower prices: The Water Authority expects prices to keep going up.

The Water Authority buys water from Northern California, the Colorado River and a desalination plant in Carlsbad. It then re-sells that water to 24 local water agencies and departments in the county.

The Water Authority expects its prices to go up 5 percent in each of the next five years, then by about 4 percent per year through 2025 and then by 3 percent each year in the future. Water officials assume that overall inflation is about 3 percent a year, so their prices outpace inflation for the next decade. (The Water Authority blames some of its price increases on rates charged by its main water supplier, the Metropolitan Water District of Southern California.)

Because demand isn’t expected to shoot up, the Water Authority may not need to invest in any major new water supply projects in the near future. In the past decade, it opened a large treatment plant in San Marcos; committed itself to buying desalinated water from a private company with a plant in Carlsbad; and raised the San Vicente Dam in Lakeside so it can store more water in the reservoir behind the dam for dry spells and emergencies.

Instead, much of the region’s new water supplies will likely come from local water agencies, like the city of San Diego’s water department, which is working on a major project to make wastewater drinkable for its customers. The Padre Dam Municipal Water District in East County is working on a similar though smaller project.

The Water Authority has explored investing in new desalination plants in Camp Pendleton and in Mexico, but neither project is considered certain.

“It’s not something we absolutely need to do in the next 15 years,” said Bob Yamada, the Water Authority’s water resources director, of the Camp Pendleton project.

Right now, desalinated water from the existing Carlsbad plant is about 10 percent of the Water Authority’s supply. Because it’s the most expensive source, though, that water accounts for 24 percent of the Water Authority’s water costs.

The long-term plan also looks at what would happen during a drought. In several scenarios that imagine a three-year drought, the Water Authority does foresee possible water shortages, especially in droughts that occur after 2025 – but that’s only if no new water supplies are added.

The Water Authority’s drought projections, though, are not ideal. The models assume that a drought will last three years. We’re now in the fifth year of the current drought.

The Water Authority will likely revise its projections again: This week, the governor ordered water agencies to plan for droughts that last at least five years.

Ry Rivard was formerly a reporter for Voice of San Diego. He wrote about water and power.

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