Carthage water is safe to drink.

The town commissioners got the good news last week from David McKew with United Water, the company that operates the town's water systems under contract.

In previous quarters, Carthage had been required to send alert letters to water customers, because the amount of trihalomethanes and haloacetic acids exceeded maximums set by law.

In fact, testing each quarter since the drought showed THMs at safe levels. The rule requires that four quarters be averaged, so it took several good quarters to meet the standard.

"The drought gave us almost a 'worst-case' sample," McKew said. "Water (from Nicks Creek) is flowing now. When it isn't moving, as during the drought, there is always going to be a bio-buildup of contaminants."

Byproducts are a natural part of water treatment. They result as a reaction between disinfectants -- principally free chlorine or a chlorine compound -- and bio-products found in the source water. Treatment with free chlorine, for example, results in the presence of two compounds: total trihalomethanes (TTHMs) and haloacetic acids (HAAs).

Carthage was under a mandate from the state Department of Natural Resources to bring down both TTHM and HAA levels based on the town's running annual average (RAA) in tested water samples.

Testing rules changed in 2005. Under current rules, trouble spots or areas of high concentrations that were previously averaged out are now considered individually and mean additional action can be required.

When chlorine is added to raw water that then is stored, there is time for more byproducts like THMs and HAAs to develop. Carthage sometimes flushes certain lines to make sure water moves enough to limit byproduct formation.

Normally, levels of total organic carbon in Nicks Creek source water are low enough that the concentration of organic materials available for disinfectants to react with and create the byproducts stays under the limits allowed.

When drought conditions caused creek water to move more slowly, there was more time for organic material to concentrate. Also, with less water used during a drought, there is more time for byproducts such as THM and HAA to be produced.

A new rule enacted Dec. 15, 2005, placed greater demands on the Carthage system. Tests had to use additional samples to predict where the highest levels of byproducts would occur. Annual averages now had to meet not only overall system targets but also individual location limits as well.

During the drought, more chlorine had to be used. That increased the level of THM as a byproduct. Test averages show that isn't happening now that water is moving more freely through the system, both at the Nicks Creek reservoir intake, through the treatment plant and water mains with less time in tank storage.

The maximum permitted TTHM level without triggering letters is .080 parts per million. Carthage water more than meets that standard, according to tests conducted by United Water. THM levels are no higher than .058, according to current measurements.

"We are now in compliance with state requirements," McKew said.

Carthage will send a letter to DENR asking the state to acknowledge the new levels.

Contact John Chappell at 783-5841 or by e-mail at jchappell@thepilot.com.