PROVIDENCE — Last week’s heat wave is causing concern among town water-supply officials and has led one of the three water districts in Smithfield to impose a system for watering outdoor lawns and flowers under which houses with even address numbers may irrigate green areas on even days, and vice versa.

David M. Powers Jr., superintendent of the Greenville Water District, which imposed the odd-even policy, said yesterday that there is no shortage of water. The problem, he said, is that most people come home from work around the same time and, if the weather is hot, many of them turn on their sprinkler systems.

Powers said that such a simultaneous demand for water could jeopardize the supply available for fighting fires.

“When you have that much water moving through the system, it becomes vulnerable in an emergency,” he said. “It’s as if everyone in town opened up their faucets at the same time. The problem is attributable to lawn sprinkling and irrigation. If the demand is sustained over a period of days, it becomes more of an issue.”

Raymond DiSanto, acting general manager of the East Smithfield Water District, said he would “perhaps need to do the same thing” as the Greenville District did.

He said all three districts get their supply from the Providence Water Supply Board’s Scituate Reservoir, so none is facing a potential shortage as are some districts in South County, which depend on wells for their supply.

“We don’t notice a shortage of water in the same sense that a district could that depends on wells,” he said. “But on the other hand we are very much aware of the fact of how much water we are purchasing, and of course in summer the water spikes.”

DiSanto said that the reservoir, which serves more than 60 percent of Rhode Islanders, is two feet lower than this time last year, according to reports. “It is a concern,” he said, but not yet cause to take any action.

Town Manager Dennis G. Finlay said the town-owned Smithfield Water District had been considering a mandatory odd-even system.

There is no crisis as of yet, he said. An odd-even order “has been a thought only because of the detrimental conditions going on in the watershed area, and the lack of rain.”

Finlay said in the past the Smithfield District did not ask for voluntary compliance with an odd-even system. “I’m not sure we would start with voluntary,” he said. “We would have to discuss it. A lot of times voluntary doesn’t seem to work.”

DiSanto, the general manager of the East Smithfield District, said that daily water is actually harmful to lawns.

“We suggest once-a-week watering for lawns, for example,” he said. “It’s a better idea than trying to water a little bit every day. It promotes a deeper root system for the lawns. If you water a little every day, the roots stay close to the surface because they are closer to the water. Then, on the first hot, dry day the topsoil dries first.”

Powers, of the Greenville Water District, said the philosophy of house construction is partly to blame for the spike in water demand at peak hours.

“Every house they build today has a huge lawn,” he said. “All the new subdivisions are heavy on lawn. So sprinkling systems can use a tremendous amount of water. Industrials do it too — if you go down Route 44 everybody wants the grass green.”

Powers said he will reevaluate the odd-even system soon. He said it probably would be lifted in about two weeks, if the area gets sufficient rain.

tmorgan@projo.com