Some Hilton Head water and sewer customers will pay about $9 more a month beginning this fall to help cope with quickening intrusion of saltwater into the island's main water supply.
The increase takes effect Oct. 15, and new rates will vary among residential and commercial users, according to South Island Public Service District officials.
The district includes Forest Beach, Long Cove, Sea Pines, Shipyard and Wexford.
"The increase is essential to provide for the district's future water supply," said Kelley Ferda, district general manager.
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The rate hike follows a study that shows the rate of saltwater entering the freshwater Upper Floridan Aquifer, the primary source of the island's drinking water, has increased because of demand from coastal communities in South Carolina and Georgia. Salt water has been advancing about 350 feet a year into the aquifer from Port Royal Sound through the north- and mid-island areas.
One of the 13 wells serving the South Island PSD has been lost to saltwater intrusion. Projections show more well failures in as little as five years, said Tobin Spirer, district spokesman.
"The rate of saltwater intrusion has accelerated faster than anticipated," he said. "There is ample water and ample time left, but we need to take proactive steps to deal with the issue. Part of that necessitates a rate increase."
Like Hilton Head No. 1 Public Service District in north-island, which has lost six wells to intrusion, the South Island PSD plans to build two aquifer storage and recovery wells.
The recovery system will store water in an underground aquifer during winter months, when demand is lower, and withdraw it during summer months, when demand rises, Spirer said.
The district also plans to improve its reverse-osmosis treatment plant, which draws water from the much deeper Cretaceous Aquifer, and upgrade its water distribution system.
The storage units and upgrades will cost about $10.5 million, to be paid for through revenue bonds.
The last rate increase was a surcharge in 2005 designed to reduce excessive water usage by customers using more than 224,999 gallons per quarter. The average quarterly home consumption is less than 40,000 gallons, according to the district.
Even with the increase, the district's rates are still among the lowest in the area, Ferda said, noting the district does not charge property taxes.
The Hilton Head service district raised taxes 12 percent in September 2010 to build its storage and recovery well and make other system improvements. The well was completed in August near Royal James Drive in Hilton Head Plantation and should be online by next summer -- a year ahead of schedule -- according to spokesman Pete Nardi. The district has said a second underground storage unit probably will be needed soon.
The South Island PSD said its recovery system and upgrades should be completed by 2015.
"There is plenty of water, but as always, conservation should be a daily watchword," Spirer said. "Water is a precious resource. Don't waste it."
Follow staff writer Tom Barton at twitter.com/EyeOnHiltonHead