If the sewer lines that run through the city of Pittsburgh suddenly shut down, every toilet from South Fayette to Ross to Monroeville would be useless.

That's why suburban municipalities should contribute to the cost of maintaining the pipes that run from the city's borders to the Allegheny County Sanitary Authority's treatment plant in Woods Run, according to an audit released by the city controller's office yesterday.

The audit calls on the Pittsburgh Water and Sewer Authority, which maintains the lines, to negotiate new agreements with 25 bordering municipalities whose sewer lines connect to the city's. The authority has old agreements with 10 municipalities and has collected $2.24 million from them since 1991.

The audit "definitely suggests that they should be paying some of the repair costs" for the city's aged lines, said Deputy Controller Tony Pokora.

Suburban reaction was lukewarm.

"We're always willing to talk about things," said Forest Hills Borough Manager Steven Morus. "Could we afford to fix others' sewer lines? There's nothing in our budget right now for that."

He said his borough faces "anywhere from $4 million to $6 million" in costs to fix its own lines through 2010.

Under a consent agreement with state and federal environmental regulators, the water authority must make repairs to its 1,400 miles of sewer lines that, in some upcoming years, will approach $20 million in cost.

Meanwhile, of the estimated 70 million gallons of sewage and storm water that enters the authority's pipes each day, around 30 million gallons comes from suburban municipalities that feed into Alcosan's plant.

If the authority doesn't get more suburban help, city ratepayers will have to bear the full cost of repairs that also benefit the suburbs, Mr. Pokora said.

The authority, he suggested, has leverage if the suburbs aren't willing to pay up. "I think the PWSA has the right and the will to shut the pipelines down, if there's no effort to reach an agreement," he said.

Authority Executive Director Greg Tutsock said the authority wouldn't shut pipelines down but would appeal to a spirit of cooperation. Suburban municipalities "have a stake in making sure these [sewer] lines work," he said. "To be partners, we have to all work together."

He said it would take time and legal research to decide how best to pursue suburban help.

Sewer providers for all 83 of the municipalities served by Alcosan are under the consent agreement, which requires a dramatic reduction in the amount of sewage that flows into the rivers. A regional organization, the 3 Rivers Wet Weather Demonstration Program, seeks to coordinate their efforts to comply.

Some suburban municipalities have already spent a lot of money on sewer repairs. Baldwin Borough has spent $12 million it borrowed from a state agency, said its manager, Tim Little.

"As far as us being able to contribute to [the authority's costs], we're just trying to hold our own in Baldwin," he said. "We had to raise taxes this year" in part to cover sewer work.

In other sewer news, Pittsburgh City Council yesterday tentatively approved a requirement that people selling homes in some communities first test for illegal sewer connections.

The property owner would have to pay an unspecified fee to the water authority, plus around $200 to a plumber who would conduct a dye test. If it turned out that storm water was illegally channeled into sewers reserved for wastewater, the property owner would have to correct that.

Authority Solicitor Clifford Levine said that under the consent order, the tests were supposed to be in place in 2004. If the state Department of Environmental Protection decided to pull the trigger, the city would owe $250,000 in fines, plus $500 per day until it complied, he said.

The testing applies only where wastewater and storm water flow into separate sewer lines. Most city homes with separate sewers are in Beechview, Brookline, East Hills, Lincoln Place and New Homestead.

Council's vote was unanimous, but members said they may amend the ordinance before a final vote Tuesday.