(Reuters) - Residents of Flint, Michigan, one of the poorest cities in the United States, paid some of the nation’s highest water bills even as the city failed to treat drinking water properly, leading to lead contamination, according to a report released on Tuesday.

The Flint River is seen flowing thru downtown in Flint, Michigan, in this December 16, 2015 file photo. REUTERS/Rebecca Cook/Files

The annual water bill in Flint as of January 2015 was $864.32 for a household using 60,000 gallons a year, said Washington-based advocacy group Food & Water Watch.

The rate remained high compared with many other cities even after a judge ordered Flint to reduce its rates by 35 percent and to stop charging a service fee.

The study - which looked at the 500 largest community water systems in 48 states - showed that private, for-profit water systems generally charged more than the public water systems that prevail around the country. Flint’s water system is public.

In a cost-cutting measure, Flint switched its water system from Detroit to a local river in 2014. The more corrosive water from the river leached lead from water system pipes, leading to unacceptably high levels of lead in hundreds of homes.

The lead contamination - which could have been prevented with anti-corrosion treatment of the water - has become a political scandal as emails and documents have emerged showing that Michigan officials tried to play down and cover up the problem for months.

Republican Governor Rick Snyder has been called to testify on the matter before a U.S. congressional committee next month. The issue has also become a focus of the U.S. presidential campaign.

The median income in Flint is $24,834, compared with $48,411 in the state, and 42 percent of the city’s population lives below the poverty level, compared with 17 percent in Michigan, according to U.S. Census data.

The second highest water prices in the country were in Bellevue, Washington, at $855.25 a year for 60,000 gallons of water.

The least expensive water was in Phoenix, at $84.24 a year.