MADISON, Wis. -- Madison Mayor Dave Cieslewicz ordered an investigation of several failures involving the chlorination of Madison's drinking water during the last year.

Cieslewicz said that he asked city engineer Larry Nelson, Paul Nehm of the Madison Metropolitan Sewerage District and George Meyer of the Board of Water Commissioners to look at the chlorination failures and how Madison Water Utility employees responded to them.

The mayor said that he's frustrated by the way the issues have been handled.

The Madison Water Utility said it uses chlorine to treat drinking water for bacteria, viruses and other contaminants.

Although the state Department of Natural Resources doesn't require such treatment, it does set standards for the contaminants the chlorine is meant to control.

Utility general manager David Denig-Chakroff said that the failures were all different, and the specific causes remain under investigation

But he said there have been improvements at the utility during the last year.