Tacoma water and power customers may soon face double-digit rate hikes, as Tacoma Public Utilities officials grapple with covering some big-ticket capital expenses in TPU’s coming two-year budget, utilities officials told me this week.

Specifics about how much exactly any prospective rate increases will be are still being worked out, as TPU prepares budget proposals to bring before the utilities board next month.

“We take any rate increase seriously,” TPU director Bill Gaines told me Thursday. “Part of our philosophy is to keep rates as low as possible.”

I met this week with Gaines and other TPU officials, at his invitation, to discuss ongoing and pending capital projects and how they fit in with the budget.

During a similar briefing he gave the Tacoma City Council earlier this year, Gaines told council members he expected rate increases to remain in the single digits. When I asked Gaines Thursday if that remains to be the case, he responded: “That’s looking increasingly difficult to do that.”

Gaines and other utility officials said Thursday they do not take rate increases lightly. They added costs for many of the forthcoming capital projects are unavoidable — coming via federal mandates or due to other requirements.

“And as for our controllable costs,” Gaines said, “we’re tying to keep those down as low as possible.”

City Councilman Ryan Mello told me Friday he’s not surprised.

“I feel like that’s how they’ve been hedging themselves,” Mello said. “I have not heard a firm number, though I’ve been trying hard to get one. But I won’t be surprised when they come before us, asking for double digit rate increases.”

Mello added TPU will have to prove to the council such rate increases are necessary.

“They will need to clearly justify the need, especially during these tough economic times,” Mello said.

Tacoma’s water and power rates remain among the lowest in the region, TPU officials have stressed. The average monthly household electric bill now runs about $104, with the average monthly water bill about $28.

We’ll have more details in a story in The News Tribune this weekend.