More than 100 customers in the Freedom District water system say their tap water has turned yellow in the last few days. But county officials have told worried callers that the discoloration does not pose a health threat.
The problem is that silt from Liberty Reservoir, the water source for about 6,000 homes in South Carroll, is rising in a seasonal act of nature. The yellow tint comes from a harmless chemical, manganese.
"The water is discolored, but there is no health hazard," said Wayne Lewns, chief of the county bureau of utilities. "We are asking for the residents to be patient. We are working at a fever pitch to correct the situation."
Liberty Reservoir, a 90-foot-deep lake on 17 acres, is about two weeks into its seasonal "turning," which could take two more weeks. Meanwhile, what is at the bottom is rising to the top.
"Any surface water turns completely twice a year," Mr. Lewns said. "Everything on the bottom comes up to the top. It is just a troublesome act of nature."
Variations in temperature cause the lake to rotate. "Come spring it will hit again," he said.
Manganese, a grayish-white chemical element, is rising to the top of the water and working its way into tap water. The chemical usually averages about .02 parts per liter in the lake. Now, as the lake turns, it is at .30, "a substantial increase," said Mr. Lewns.
"It is not poor-tasting, but there is discoloration," said Robin Pirone, a resident of Carroll Highlands. "The water in the bath, sink and toilet is yellow."
The county has offered to test Ms. Pirone's water to reassure her of its quality.
Mr. Lewns said his office has received dozens of calls this week, most from newcomers to South Carroll.
"If people are not used to the problem, it upsets them," said Mr. Lewns. "The old-timers know what is happening and don't bother to call."
Mr. Lewns has seen the problem recur many times since he began working at the county water department 20 years ago.
Crews are working around the clock to restore the lake's clarity. Ms. Pirone said yesterday she has noticed an improvement.
Clarifying the reservoir is a trial-and-error system, Mr. Lewns said. Permanganate, the first chemical tried, had no effect, nor did a combination of chlorine and lime. Workers are testing another chemical agent and finding some success.
"Once we find which agent restores the clarity, we will go through and flush the entire distribution system," he said. "We are seeing an improvement with Sequestor. Once that improvement intensifies and as soon as the turning stops, we'll flush."
How long will the turning last?
"You would need a crystal ball to predict," said Mr. Lewns. "If the extreme cold last week had lasted longer, it would have shortened the turning."