FLINT, Mich. — As Detroit seeks to settle its debts and chart a viable course for the future, one of its best sources of revenue, clean water for sale, may be evaporating.

The fresh water in Lake Huron is still plentiful, but the customers are having second thoughts about Detroit and its vast, aging water system.

Detroit pipes much of its water from the lake, and Detroit Water and Sewerage, the city’s water department, sells it wholesale across southeastern Michigan, generating about two-thirds of the city’s water revenue.

But this year, Detroit is losing its second-biggest customer, the City of Flint, which has joined with surrounding Genesee County to build a $300 million, 63-mile pipeline parallel to an existing one to bring water directly from Lake Huron, cutting out Detroit.