KAPAIA, Kaua'i — Treated surface water has started flowing into the Hanama'ulu water system, with the opening of the main valve from a new water purification system.

Water from the old Lihu'e Plantation Co. irrigation system is being run through an advanced membrane filtration system that allows water to pass through while leaving impurities behind. The water is chlorinated to kill any organisms tiny enough to pass through the filters.

Grove Farm Co. built the $9 million system to meet water supply requirements for Grove Farm and Lihu'e Land Co. developments planned from Puhi to Hanama'ulu. Grove Farm owns the facility and contracts Aqua Engineers to operate it. The county Department of Water is its sole customer.

The Lihu'e region previously was supplied primarily from wells. The new plant, along the Kapaia Reservoir off Ma'alo Road, is rated to treat up to 3 million gallons a day but won't reach that capacity until summer. It will be the regional water system's single largest source of water.

The treated water, which started running this week, initially will serve only the Hanama'ulu area, but as production rises over the next several months, the water will be fed into water systems to the north and south of the community.

Department of Water manager Ed Tschupp said that for safety reasons, chlorine levels will be a little higher than normal during the phase-in period.

The Lihu'e area has been under development restrictions because of increased demand for water and reduced supply. "The productivity of our existing wells has declined," Tschupp said.

Engineers found that many of the shallow wells in the area had been recharged in part from plantation furrow irrigation practices. When the plantations switched from furrow to drip irrigation, and then went out of business, recharge of groundwater sources under the cane fields declined and well yields dropped.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.