GREENVILLE — A combination of chemicals used in hundreds of water-treatment systems across the country could cause lead to leach into drinking water from plumbing, UNC-Asheville researchers say.

Richard P. Maas, an environmental science professor, said the chemical interaction could cause elevated lead levels like those that have plagued Greenville recently. At least 20 of the state’s 7,700 public water systems use the chemicals, including those of Raleigh, Cary and Johnston County, according to state records.

About 500 systems across the country have switched to the so-called chloramine treatment since 2001, Maas said, to meet federal requirements.

“We suspect there are hundreds of other towns out there whose tap water lead contamination has gone up substantially but have not come to light yet,” he said.

Pitt County health authorities earlier this month issued a lead advisory for water from the Greenville Utilities Commission, which serves about 70,000 people. Testing showed one child had lead poisoning and another had elevated levels. Even small amounts of lead can cause neurological damage in children.

State officials said they are reviewing the water treatment and lead testing at other systems in light of Greenville’s problem.

“Greenville is sort of like a wake-up call,” said Ken Rudo, a toxicologist with the N.C. Department of Health and Human Services.

If high lead levels show up in other systems, Maas said, “that might be very indicative that a very specific cocktail, so to speak, is causing a problem.”

State agencies will review Maas’ research and data from water systems, he said, which could take two to three months.

Federal regulations require that large water systems test for lead in a sampling of homes every six months. If no problems are detected, the testing occurs every three years.

Kelvin Creech, Cary’s water plant manager, said the town detected one incident of elevated lead in 2003, a condition attributed to lead solder in an older home. That was corrected by replacing pipe joints, he said.

“We’ve really not had a system problem,” he said.

Larry McMillan, laboratory supervisor for Raleigh’s water plant, said the city’s most recent tests were in 2002. He said the system, which serves about 344,000 people, began using the chloramine treatment in 1993 and testing has not detected lead levels above the federal standard of 15 parts per billion.

Johnston County reported no lead in excess of federal standards in a 2003 water quality report posted on the county’s Web site. “We’ve never had any problems,” County Manager Rick J. Hester said Tuesday.

Homes built before 1986, when lead solder was banned, have the highest risk of lead, but Maas said meters and plumbing fixtures in most homes contain lead that could leach into the water.

Rudo, the state toxicologist, said Tuesday that the department recommends that customers have water tested if it has an odor or unusual color.

He repeated the state’s warning for Greenville water, especially for pregnant women, breastfeeding women and children under 6. Tap water there should not be used for drinking, cooking, preparing formula and brushing teeth until it is tested, according to the advisory.

Maas and Steven C. Patch, co-directors of the Environmental Quality Institute at UNC-Asheville, said their research showed that a combination of chloramines and fluorosilicic acid, especially with extra amounts of ammonia, increases lead leaching. Chloramine is a combination of chlorine and ammonia, and is added to disinfect water. Fluorosilicic acid is often added to water to improve dental health, a process known as fluoridation.

Tests showed lead levels three and four times higher in water with that combination of chemicals, he said.

About 500 systems across the country have switched to chloramine treatment since 2001, Maas said, and most also use fluorosilicic acid.

He said the institute’s lab has tested more than 150,000 homes across the country in the past 18 years and found that 10 percent to 15 percent have a significant lead contamination problem.

Maas, who heads a lead poisoning prevention program in Western North Carolina funded by the federal Centers for Disease Control and Prevention, said there should be more monitoring of lead in drinking water. The good news, he said, is that high lead levels in tap water can be easily lowered by running water for at least a minute before using it; this flushes contaminated water.

He said homeowners should have their water tested — a process that costs from about $20 to $100 — to determine whether lead is a threat. Water filters attached to faucets also remove lead when the filters are properly maintained, he said.

The Greenville Utilities Commission has been trying to determine the cause of the lead problem since last year, when elevated levels showed up in 26 of 106 sampled homes. Officials said water leaving the plant and its distribution lines do not contain lead.

About 300 customers had water tested after notice of the lead was issued in November, and levels were high in 25 percent of the houses. About 530 more requested tests since the advisory. Results from 11 have been returned, a commission official said Tuesday. One of those showed an elevated level.

Barrett Lasater, director of water and sewer treatment plants for Greenville, said local officials would like to review Maas’ findings. But he said other cities that treat water as Greenville does have not recorded elevated lead.

“You would think you would have seen it in more than us,” he said.