CHICAGO (CBS) — The city of Chicago is looking for volunteers who want their water tested for lead, but for this testing, don’t call the city, the city will call you.

It’s apparently an assumption in the industry, among those who know how water systems work; if you replace an old water main with a new one, then the houses it’s hooked up to will have higher lead levels.

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However, Gary Litherland, spokesman for the Chicago Department of Water Management, said it’s an unproven assumption; not proven here or anywhere.

“There is a widespread suspicion in the industry, but it’s an assumption, and that’s the unfortunate part,” Litherland said. “Everybody’s taking the assumption of elevated lead levels due to construction, because it just seems to make sense, and we understand that, but a lot of things have been assumed that have been proven to be false.”

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So, beginning later this year, Chicago will be asking people, street-by-street, if they want their water tested for lead – right before the city replaces the main in the street, and again right after.

“We’re looking for real data,” Litherland said.

Separate and apart from that water main work, Litherland said about 2400 people in the city have asked that their water be tested for lead. Less than 3 percent have had elevated lead levels.

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The city is being sued by some residents who say the water main work has put them at risk.