TAMUNING, Guam — Guam’s water is safe to drink, said the local official in charge of the water and sewage on the island. But convincing people of that is another matter, he’s acknowledged.

“Probably most people drink bottled water,” John Benavente said in June. He’s general manager of Consolidated Utility Services, which includes Guam’s power, water and sewage systems.

A bad rap is just one more challenge for an antiquated utility system needing repairs and restructuring to better meet the needs of its 39,000 water customers, 21,000 sewage system customers and 46,000 power customers, according to local officials.

Yet there’s one customer among those thousands, local officials say, whose size, demand and wealth could help spur some of the improvements: the U.S. Department of Defense.

The military here is the No.1 customer for the Guam Power Authority, consuming 16 percent of the island’s energy and accounting for 20 percent of the authority’s sales receipts, according to Joaquin “Kin” C. Flores, general manager for power.

The military also buys water from Guam for Andersen Air Force Base, Benavente said. Parts of southern Guam still rely on Navy resources for water, though Guam Waterworks pumps and delivers those 5 million gallons daily.

But as 8,000 U.S. Marines and more than $10 billion of military investment make their way to the island in coming years, local utility officials see an opportunity to expand their system, enlarge their customer base and share some of the costs to do both.

Expected population growth and the military buildup will require another power plant and possibly more efficient and reliable ways to pump water and sewage throughout the island, Benavente and Flores said.

So power and water officials met with local military leaders in March to discuss the utilities’ improvement plans and concerns about reliability and recovery, especially involving typhoons.

“We have agreed to closely work together,” Benavente said. “We do want to be able to service the military.”

Exact utility needs for the military’s expansion are unclear at this point. Flores and Benavente said local officials are open to discussing other ways to tap into Guam’s system. Flores said they’ve begun meeting regularly to discuss everyday concerns and improvements.

A comprehensive plan is forthcoming, but no date has been set for its public release, U.S. Pacific Command officials said.

Guam’s utilities governance has undergone substantial change in the past three years. Governor’s-office appointees formerly controlled the utilities, a system rife with internal politics and little long-term vision, Flores, Benavente and others said.

Now, an independently elected board controls them. For the first time, both power and water departments have developed long-range plans and begun to borrow the money needed for the billion-dollar projects.

The water authority’s long- term goals are court-ordered. It has been fined $110,000 in the past few months for failing to meet some of its planning deadlines. For more than a week, residents in southern parts of Guam have been living with water restrictions or dry taps.

Still, the authority was able to sell $100 million in bonds last winter, a substantial start toward improvements, Benavente said. And it’s operating in the black for the first time in years, he said.

Both power and water systems also can withstand a population increase for the near and distant future, both men said. The power authority is using just half of its current capabilities each day. The natural aquifer below northern Guam, which supplies most residents with water, also could double production without harming the resource, Benavente said.

But problems remain. The power authority needs to improve its ability to recover after a typhoon. Most of the power plants, distribution points and even household lines are above ground, Flores said. The system’s reliance on fuels costs everyone. Base fees have remained stable for 10 years, but fuel prices have tripled in the past three years, he said.

Andersen Air Force Base, at the island’s northern end, gets all of its power, water and sewage services from Guam’s local system. The U.S. Navy buys power from Guam but has its own water supply, Fena Reservoir. The Navy sells some of that water to Guam for residents and businesses in the island’s southern region.

It’s that water supply that has been causing residents in areas, including Santa Ritaand, Agat and other areas, to live with limited water for more than a week. Heavy rains tax the Navy’s ability to treat water from the reservoir. As of early this week, the Navy was supplying Guam Waterworks with a little more than half as much water as normal.

Being able to more easily funnel northern well water to southern homes would alleviate these shortages, Navy and Guam officials have said.

“We recognize we have a lot of work to do,” Benavente said. “We recognize we need to get up to speed.”