The drinking water for an estimated 400,000 people around Charleston comes from the Bushy Park reservoir.
Since November, 17 alerts have been sounded that salt water was creeping close; more freshwater had to be released from depleted Lake Moultrie, the drinking water for nearly a half million more people.
That tenuous give and take drives home just how serious the drought has become in the Lowcountry.
Alerts aren't unusual this time of year along the tidal Cooper River where Bushy Park is located. But the number is three or four times as many as usual since Santee Cooper in early October was allowed to cut back the flow from the lake's Pinopolis Dam, to help conserve its water, said David Hubbard, operations branch chief for the Army Corps of Engineers, Charleston District. The Army Corps regulates the dam spill.
The cutback is to make sure the lake — now lower than any time except once in its half-century history — continues to have enough water. And that's partly to make sure water can be released to protect Bushy Park.
"It's something that has to be watched very carefully by all of us," said Andy Fairey, Charleston Water System chief operating officer. "When you get down to the drought we're in, it's a matter of everybody watching their water intake."
"I think it reinforces why water and electricity are precious commodities in this state," said Laura Varn, corporate communications vice president for the Santee Cooper utility, which operates the Lake Moultrie Water System.
The situation is approaching the worst stretch of the 1998-2002 drought, when salinity alerts became regular. Water managers stressed that public water supplies are not in jeopardy. The lake still has plenty of water.
"This is not a major problem. These are alerts for Santee Cooper to push that salt level downstream so it won't be more of a threat," said Hubbard of the Army Corps. "It's not life threatening. It's not drinking water threatening."
The alerts partly have been a consequence of unusually high fall tides that pushed the salt water line farther upstream, he said. The salinity levels that trigger alerts are set to protect equipment of industries along the river that have a lower tolerance for salt water than the Bushy Park treatment plant. And the plant is located on Back River farther upstream.
But the state is in a severe drought, with rainfall since the first of the year ranging from 10 inches to more than 21 inches below normal. Even after the weekend rain, Charleston is 10 inches below normal.
The weekend rain dropped as much as 2 inches across the Midlands, said Hope Mizzell, state climatologist. Those streams, which feed Lake Moultrie, have risen somewhat and are expected to stay up for awhile because dormant trees make less demand on groundwater. "This time of year we do see some benefit from every rain event, especially rain more than a half inch," Mizzell said. But the weekend rain fell nearly two months after the most recent previous rain. "We can't go another two months before another rain event. We need to see rain every four or five days."