DURHAM - Durham has passed a federally mandated test looking for lead in its water supply, but city officials cautioned residents Monday to continue precautions when consuming water from household taps unused more than six hours.

The U.S Environmental Protection Agency requires public water systems to survey selected residential taps every three years. Durham had last conducted the tests in 2004 but was asked to perform them again a year early after concerns were raised about the chemical process used to treat the city's water.

Those concerns heightened in April, after a child was found to have lead poisoning. Water drawn from the kitchen faucet in the South Durham apartment where the child lived was found to contain the toxic metal in concentrations nearly 60 times the federal safety limit.

Further testing by the city and the county Health Department found lead in water from dozens of homes scattered across Durham. Drinking fountains at eight schools were disconnected during the summer after lead was found in unacceptable amounts.

Lead is especially dangerous to young children and fetuses, causing developmental difficulties and brain damage.

In July, the city ceased using a chemical, ferric chloride, in its water treatment amid concerns that it was helping lead leach from old plumbing fixtures and pipe solder.

Federal rules do not require the city's water to be lead-free but rather to test within acceptable limits. In September, Durham collected samples from 69 homes picked because they were built between 1982 and 1985. A federal ban on lead in the solder used to join copper pipes went into effect in 1986, and homes built just before the ban are considered to be most at risk.

High levels

According to a statement the city released Monday, four of the Durham homes -- about 6 percent of the total -- were found to have lead contamination at 15 parts per billion or above, the level considered dangerous. Federal guidelines allow up to 10 percent of samples to be above the limit before a city is deemed to be out of compliance.

Efforts to reach Terry Rolan, Durham's director of water management, were unsuccessful Monday. A city spokeswoman said Rolan, the president of the American Water Works Association, was not in town.

The city news release Monday quoted Rolan as saying he was pleased with the results. But Rolan also urged Durham residents to continue letting their water run for several minutes before drinking from a faucet that has gone unused for more than six hours -- a precaution shown to flush out potentially contaminated water.

Change cited

Marc Edwards, a Virginia Tech scientist who tested Durham's water last spring after being hired by the owners of the apartment complex where the poisoned child had lived, said Monday the change in the city's water chemistry may explain the good news on lead levels.

Durham stopped using ferric chloride after Edwards' research suggested it was making the water corrosive. Durham had used ferric chloride as a coagulant at one of its two water treatment plants since 2003.

"From the time the corrosivity of water is reduced to the time you get very low lead can be only a few weeks to months," Edwards said.

The Durham child found to have been poisoned in April was only the second such case in state history to have been conclusively linked to a municipal water supply. The first was a Greenville boy diagnosed in early 2005.

Falling in Greenville

The city of Greenville, which altered its water treatment process on Edwards' advice, is finally seeing lead levels in its drinking water fall, said utility plant manager Barrett Lassater. It hasn't met EPA requirements for minimum amounts of lead detected at drinking taps since 2004 but expects to pass next month, he said.

Laura Leonard, the spokeswoman for the state Division of Environmental Health, said state regulators have not yet reviewed Durham's latest test results. The samples were screened for lead at a city lab rather than a state facility. That review will determine whether Durham is asked to conduct further tests in the coming year, Leonard said.