The downtown Chicago skyline.
The downtown Chicago skyline. - 
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It’s a classic homeowner’s dilemma: Try to fix one thing, break something else. Chicago Mayor Rahm Emanuel has been upgrading the city’s water system. But a new study from the Environmental Protection Agency suggests that work may be causing new problems -- by disturbing lead pipes that lead to people’s homes. 

The problem is what are called “service lines.” As late as 1986, they were often made of lead. The EPA study indicates that when construction work -- like replacing a water main -- touches a service line, the risk of serious lead contamination skyrockets. And sticks around for years. 

What would it cost to dig up all those service lines? "That's a huge expense," says Rick Andrew, an expert on water quality and treatment for NSF International, a non-profit that develops standards for water and food safety. "Especially a city like Chicago, where most of the buildings were built before the 1980s."

And if you live in an older house in Chicago, and they're tearing up your street -- how much would a water filter cost you?

Andrew Wilson, from suburban Angel Water, offered a high-end pitch: "Usually, a high-quality system to remove lead out of the water would run a family, to have it installed by a licensed plumber, around $1,500. 

Follow Dan Weissmann at @danweissmann