Tucson Water officials are investigating how a treatment plant sent water contaminated with chemical compounds to thousands of residents of the city.
Reports say that utility officials mistakenly thought that uncontaminated water was coming out of the plant, which has long treated water pollution on Tucson's south side.
Authorities say the utility had been sampling the water at a point its officials thought was connected to the treatment plant, but which actually was getting water from other sources.
According to the report, the levels of the chemicals found in the water coming from the treatment plant were lower than the recommended maximum in federal health advisories.
The plant's water is sent to about 60,000 residents of downtown Tucson and the city's west and north sided.