An ordinance requiring protective valves on water connections to prevent contamination of the city's drinking water has been approved by the City Council.

The ordinance requires back-flow valves, which prevent water from flowing backward from pipes on users' property into the city's system, on connections the city's public works director determines may be hazardous.It requires the valves, which cost from $15 to $150 for residential-size units and up to $1,000 for high-pressure, larger ones, to be inspected and certified as operational annually, a cost estimated by Public Works Director Randy Randall at $50 to $100.

Randall said his first enforcement priority will be major water users with the greatest potential for contaminating the city's water supply, such as industrial and commercial users, schools and churches.

But Randall estimated there are up to 250 homes in Centerville that have cross connections, which he defined as being hooked up to the city water supply and also having a separate supply, such as a well.

Those homes should also eventually be required to install back-flow valves, Randall told the council.

Contamination can occur in a number of ways, Randall said. A drop in the city's water pressure can cause water to flow backward briefly, sucking it out of homes and businesses and back into the city's system, spreading the contaminated water throughout the city.

He cited cases from around the country where contaminated water has been drawn into city systems.

It's possible, he said, for a homeowner spraying his yard with weed killer using the new, popular hose end sprayers to contaminate his own, and part of the city's, water supply.

To prepare for enforcing the ordinance, Randall and two of his department employees have been certified as back-flow valve inspectors.

But Randall said full enforcement, including notifying users they need to install the device, checking for compliance, and the annual inspection, will require more man-hours than his department can supply.

Although agreeing the city is not prepared yet for full enforcement of the ordinance, the council approved it, saying protection of the city's water supply is crucial.

The council agreed the ordinance should be on the books, ready for enforcement, and directed the city staff to draft an implementation plan.