The Dallas City Council on Wednesday authorized city staff to meet with Irving officials to seek a short-term solution to the town's water shortage.

Irving has informed Dallas Water Utilities that it might need to purchase significant amounts of Dallas water – perhaps tens of millions of gallons a day – because Irving's primary water source, Lake Chapman in northeast Texas, is dwindling.

Irving Mayor Herbert Gears said his city might be unable to extract water from the lake after May, depending on rainfall.

By state law, if Irving needs water, Dallas has to provide it – a responsibility that comes with being a regional water provider. But Dallas officials are concerned that the extra demand will force water restrictions on their own constituents and other Dallas water customers.

"Our customers will feel an impact," Dallas City Manager Mary Suhm said.

Dallas City Council member Ed Oakley said the two cities will find a short-term solution for the drought. One might involve Dallas leasing some of Irving's equipment at Lake Chapman to store and transfer water.

But Dallas could find itself in a quandary if other cities and water districts also request additional water. The North Texas Municipal Water District, also struggling to service its customers, has arranged similar talks with Dallas.

"If we're forced to let other people tap our reservoirs, we're going to have to find other resources to replace them," Mr. Oakley said. "That's exponentially more expensive in today's dollars than when we built these reservoirs."

Mr. Gears said Irving hates to be an inconvenience but its options are limited because of the drought. He said Irving is trying to give Dallas as much notice as possible about possibly requesting more water.

"We want to do everything we can to make sure we're not creating a negative consequence for Dallas Water Utilities," Mr. Gears said.

Lake Chapman is 83 percent depleted, according to a Dallas memo.

Irving, which already buys roughly 10 percent to 20 percent of its water from Dallas, could need an additional 63 million gallons a day on peak use days – the amount that it gets from Lake Chapman.

Irving officials said it's too early to say exactly how much water they'd need. They wouldn't speculate about how much they might have to pay for the additional Dallas water.

The Dallas City Council met behind closed doors Wednesday to discuss how to respond to Irving and other cities' future water needs.

Several Dallas council members said the city spent decades – and hundreds of millions of dollars – ensuring that its constituents and customer cities could withstand major droughts without serious water cutbacks. They worry that unanticipated water sales to Irving will force Dallas' other customers to face harsher water restrictions in coming months.

Dallas entered Stage 1 of its drought contingency plan in October, months after many of its peer cities. Since then, the city's water levels have remained 35 percent depleted, even after recent rains. Dallas already anticipates triggering Stage 2 water restrictions by June.

Irving, meanwhile, plans to implement Stage 3 water restrictions at the end of November – and additional restrictions could be on the way. Stage 3 restrictions include limits on landscape watering to no more than twice weekly, with no watering allowed between 10 a.m. and 6 p.m. No refilling of swimming or spa-type pools is allowed. No washing of sidewalks or driveways is allowed.

The city is also considering hiring a consultant to look for additional water sources. The city's strategic plan calls for assuring a "dependable water supply for Irving beyond a 75-year period."

If enough rain fills Lake Chapman in the next several months, "this becomes a nonissue," said Jim Cline, Irving's public works director. But Irving is working with Dallas to devise a solution that works for both cities, he said.

"I feel very confident that there will be water for the citizens of Irving," Mr. Cline said. "We'll provide an adequate and safe water supply for the citizens."

Irving spent more than $100 million to build a pipeline to Lake Chapman to lessen its dependence on water from external sources such as Dallas. Irving started getting Lake Chapman water in 2003.

Irving City Council members recently gave city staff informal approval to work with the North Texas Municipal Water District on a dredging project at Lake Chapman. The project might cost the city about $1 million, city officials said.

Ms. Suhm said Irving is going to need help – and Dallas isn't in a position to say no.

"They've put in restrictions; they're dredging," she said. "But that lake is basically dry."

In other Irving water news, the City Council said Wednesday that it's delaying a vote on a $300,000 contract to hire Dean International to find new water sources.

Irving wants Dean to create a "comprehensive analysis of water-related assets," including city water sources, major transmission pipelines, water rights and water access agreements.

Some council members want more information, Mr. Gears said.