Crews are replacing lead and galvanized steel service lines in 788 Flint homes as part of the city's plan to fix a lead-tainted water crisis.
Mayor Karen Weaver says Monday that one company already is switching out some lines, while a second firm on Tuesday will begin replacing lines that lead from water mains to residential meters.
Weaver's FAST Start initiative is being paid with $25 million from the state. Water lines were replaced in 218 homes during phase two.
Flint was under state financial control in 2014 when it switched from Detroit's water system to the Flint River to save money. Officials failed to treat the river water with corrosion-control chemicals which allowed lead to leach from pipes.
Flint has since returned to Detroit's water system.
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