Lead solder, which studies have blamed for concentrations of the element in tap water, will be banned for use in plumbing installation in Montgomery and Prince George's counties starting April 1.

Based on tests of water in new houses here, the bicounty Washington Suburban Sanitary Commission voted last month to ban use of lead solder and flux to join pipes. Existing plumbing is not affected by the order.

Maryland health officials recently found levels of lead ranging from 10 to 150 times the federal safety standard in tap water in a sample of five new houses in upper Montgomery where lead had been used on copper pipes.

A statewide ban is under consideration by the Maryland State Board of Commissioners of Practical Plumbing, which has scheduled a vote on the issue April 24. Lead is already banned for plumbing in Baltimore County.

A similar order also will go into effect in Virginia April 1.

Lead is a poison that accumulates in the body and leads to such health hazards as retardation and behavioral problems in children, kidney damage, irritability, insomnia and high blood pressure and joint, stomach and head pain.

Health officials say that concentrations of lead tend to build up overnight in pipes. Allowing tap water to run a few minutes in the morning reduces the amount of the element to safe levels, they said.

The state tests conducted in Montgomery were the first in a series planned by Maryland health officials. Ray Feldmann, a spokesman for the Maryland Office of Environmental Programs, said the five houses were less than a year old and were in housing developments between Gaithersburg and Poolesville. Three of the houses were vacant.

"We made recommendations to the people in the occupied houses that they should, at this point, let the tap water run three to four minutes," Feldmann said.

"In our study we did it for 10 minutes, but at this point we don't feel it's necessary for the homeowner," he said.

Although all the lead levels recorded in the houses were much higher than the U.S. Environmental Protection Agency lead-content limit of 50 parts per billion -- it was measured at 7,710 parts per billion in one unoccupied house -- the levels dropped below 10 parts per billion in each case after the water was left running 10 minutes, officials said.

"They don't have to turn on every tap in the house; just one tap," Feldmann said. "That should bring the levels down to well under the 50 parts per billion."

Residents of houses older than two or three years need not worry, EPA and state health officials said. After several years, accumulated mineral deposits on the inside of the pipes protect the water from contamination.

For the initial years, said EPA spokesman Joseph Cotruvo, residents should "get into the habit of taking a shower or flushing the commode in the morning before drinking the water. That purges the line."

Cotruvo said several states around the country are taking action to ban lead solder and flux, as health officials become increasingly aware of the problem.