It’s hard to imagine a California summer without long days lounging by the pool. But as unprecedented drought sears the state, the backyard swimming pool has become a target for cities desperate to save water.

As cities and water districts put the squeeze on water users, even pool lovers are canceling construction contracts. Pool builders are steamed, accusing water officials of stressing symbolism over science. And contractors are getting increasingly creative in finding sources of water for pools that cities won’t fill.

The new restrictions — largely the result of Gov. Jerry Brown’s order to cut water use 25 percent statewide — have become a nightmare for Bay Area pool builders and hot tub retailers.

“It keeps me awake at night,” said Marc Hannigan, who manages pool building companies in Pleasanton and San Jose. “If this goes on, we’re going to have to find a different line of work.”

San Jose recently became the largest city in the state to ban filling pools and outdoor hot tubs. Under the new restrictions, the city’s homeowners may top off pools with only one foot of water unless a pool needs to be drained for sanitary reasons or to repair a leak. Filling a new pool is a total no-no. Scofflaws face fines of up to $160 per offense.

San Jose joins Santa Cruz, Morgan Hill, the Dublin San Ramon Services District and at least a dozen other California cities and water districts that outlaw filling pools. The city is “hitting the pause button” on all major water uses, including summer landscaping projects as well as pool filling, Mayor Sam Liccardo said in an interview.

“We don’t know whether the rains will come next year or the next decade,” he said. “If we don’t take aggressive action today, the pain will be far more widespread.”

But Hannigan said he’s already felt his fair share of pain. Half a dozen of his customers, he said, have withdrawn from contracts in the past two months. Even before the new restrictions made things worse, he said, his business was down 30 to 40 percent because of the Great Recession and drought.

The new rules have made pool builders as resourceful as they are desperate. To get a permit to build a pool in Dublin, Hannigan had to make a deal with the city. He is going to drain an existing pool undergoing renovation — and then truck that water to the construction site to fill the new pool. The pool and spa industry has also been working overtime to change the public perception of pools and hot tubs as an extravagance during a drought.

“Because our product is full of water, a lot of people feel like it must be a waste of water,” said Keith Harbeck, president of Premier Pools and Spas in Sacramento. “That’s just not true.”

Filling a new pool can take 20,000 gallons up front but actually saves water in the long run, Harbeck argues. That’s because pools usually replace water-guzzling backyard lawns with hundreds of square feet of patio or decking. A typical pool uses 30 percent less water each year than the lawn it often replaces, according to a frequently cited study by the Santa Margarita Water District south of Los Angeles. With a pool cover, the pool uses less than 5,000 gallons a year, 80 percent less water than a lawn, the study concluded. Amazingly, the study even showed that a pool can be as water-efficient as drought-tolerant shrubs and trees in the long run.

San Jose water officials, however, are not convinced, pointing out that it takes three to five years for the savings the pool industry cites to get back the water poured into a pool when it’s first filled. And, officials say, the city needs to save water now. For their part, some hot tub retailers resent that their product is being lumped in with pools.

Lynda Sisk, vice president of Hot Springs Spas of San Jose and Santa Cruz, said she uses her hot tub several times a week and has to add only 10 gallons a month. Most of her customers use their spas for therapeutic reasons, she said, and they would otherwise turn to long, wasteful showers to ease aching muscles and joints.

Sisk believes cities should let residents choose how to conserve: “Tell me how many gallons I can use; don’t tell me how to use it.”

In part because of Sisk’s heavy lobbying, Santa Cruz eventually decided to remove the spa-filling restriction from this year’s drought regulations.

Harbeck called bans on filling swimming pools equally “misguided.” Given the tiny percentage of water a city uses for pools, he said, “it’s kind of a symbolic gesture.”

In response to the pool industry’s lobbying, the city of Santa Barbara last week decided to step back from a proposed ban on filling pools. City officials cited evidence that pools use only 0.001 percent of the city’s water supply.

But other cities are ratcheting up the restrictions. Milpitas, for example, has stopped issuing permits for new pool construction, though exceptions have been made if water will be shipped in from elsewhere. So far, however, San Jose has no plans to halt pool construction, officials say.

The city issued 49 permits to build new swimming pools in the 13 months since the Santa Clara Valley Water District and the San Jose Water Co. first banned filling pools in March 2014. In the week after the city’s April 21 drought ordinance banned pool filling citywide, the city issued six more permits for new pools. The city doesn’t want to interfere with construction more than necessary, Liccardo said.

“You can construct a pool and use it for a skateboard rink,” he said. “You can fill it with recycled water. You simply can’t fill it with potable water.”

Contact Nicholas Weiler at 408-920-5764. Follow him at Twitter.com/Lore_Nick.