The department last week lifted a mandatory drought restriction on the Upcountry water system, with demand on the system remaining below 6 million gallons a day and with steady rains restoring water flows.

But Eng continued an appeal for consumers on the Central Maui system, which serves the area from Pa'ia to Wailuku to Kihei, to curtail daily use by 10 percent.

"Water demand countywide was lower due to wetter and cooler weather. The community's growing consciousness in water conservation is certainly also an important factor," he said.

After peaking at more than 28 mgd during the summer, demand on the Central Maui system has been averaging less then 20 mgd for the past three weeks — well below the conservation target set by Eng of 25.5 mgd.

But he said Central Maui consumers need to continue the low use to help maintain demand at or below the target to meet a 12-month moving average, the water- use limit established for the existing sources.

"Basically, that number, 25.5 million gallons a day, is what we are allowed to take," he said.

The Central Maui system relies on three sources — the 'Iao aquifer, the Waihe'e aquifer and a treatment plant on the Kama Ditch diverting water from the 'Iao Stream.

The 'Iao aquifer has been designated for strict oversight by the state Commission on Water Resource Management with a cap on use at 20 mgd. The commission also set a limit of 4 mgd for pumping from the Waihee aquifer. The water department has a capacity of just over 1.5 mgd at the Wailuku treatment plant.

The limits on pumping in the 'Iao and Waihe'e aquifers are based on what the commission calls a 12-month moving average, essentially an annual average daily use. That allows pumping in some periods to exceed the limits, as long as lower demand in other periods balances the high pumping periods.

"The lower demand offsets the high pumping in the 12-month moving average," Eng said. "This is the time of year when demand is down, that we get to offset the heavy pumping during the dry season.

"It allows the aquifer to recover, and the regular rainfall helps to recharge the aquifer."

But consumers need to maintain the lower demand for at least as long as high demand during the dry season exceeded the limits. There is also a concern that lower-than-normal rainfall for the past several years may be affecting recharge – the amount of water percolating through the ground of the watershed into the aquifers.

Torrential rain events, such as the Dec. 5 Kona storm, are not especially helpful to the system because more water will run off than will penetrate into the watershed. Heavy rainfall also will pick up more dirt and debris, increasing turbidity in surface water systems and affecting the capabilities of treatment plants taking water directly from ditches such as the Wailuku plant or the treatment plant at Kamole Weir in the Upcountry system.

While encouraged that consumers appear to be taking conservation more seriously, Eng said the department is having to consider how and where it can develop new sources of water.

"It's now real challenging. We had looked at going into the north Waihe'e aquifer, but we have a report from the U.S. Geological Survey that the yields are not going to be that great," he said.

For the water department, source development needs to balance costs against benefits. Extending water transmission lines generates costs for easements, construction, maintenance and operations that increase the farther the source is from the users. Those costs need to be weighed against the amount of new water produced.

But where there is easier access to water sources, there is also increased competition. Eng noted that the department is studying another well at Waikapu, projected to have a potential yield of 2 mgd. But the investment group that has acquired the former Wailuku Sugar Co. lands from Waikapu to Ma'alaea already has applied for a well permit in the same area.

Groundwater systems in the East Maui watershed are projected to have significant capacity to provide new water, but former Mayor Alan Arakawa five years ago signed a consent decree that restricts the county's ability to develop East Maui aquifers without detailed scientific data on the impacts on overall water systems.

"People realize that East Maui has the most abundant water resources, but there are legal issues that need to be addressed and that will take time to resolve," Eng said.

In the short term, he said, the most feasible new sources for the county may be to tap brackish wells and desalinate the water.

"I didn't think I would say this, but that appears to be the most reasonable option for new sources within a short time. The question will be finances, how much will it cost," he said.

The other option is to say there is no more water, a situation that will block further development by small landholders and developers who have no access to water sources.

"We're always talking to the elected officials about that," Eng said.