The City of Mercer Island just sent out its annual water report to all water consumers on the Island, as required by law. What does it show?

Inspections reveal that the water quality is good, with only very minute sources of toxic substances detected. The sources of water for the Island are stable, shored up by the new emergency well.

The annual report is required by law along with five-year inspections of the system conducted by the state Department of Health. The state DOH reported that the city’s system was operated and maintained adequately.

The city purchases water from the City of Seattle. It comes from the Cedar River Water supply via the Seattle Public Utilities water transmission system — a pipe under the lake. That water is treated and tested by SPU prior to transmission.

There are a few trouble spots, including a puzzling difference between the amount of water purchased from the City of Seattle and the amount billed by the City of Mercer Island. The city purchased 640.5 million gallons from Seattle — but some 4 percent more was shown on customer meters and billed.

City maintenance director James Mason, said that  just a month ago engineers found the discrepancy and are working to resolve it. It is  probably due to metering issues on the SPU side of the pipe, he said.