MOUNTAIN HOUSE — Disputed late fees on Mountain House water bills have become so common that the town’s administrators have pledged to track down the accounting errors.

Mountain House homeowners are growing more frustrated after they mail water bill payment checks on time, only to learn that the town’s water company, ECO Resources Inc., does not record their payments until after the due date.

Fed up with the epidemic of delinquent account notices, a group of frustrated homeowners met Thursday with Paul Sensibaugh, general manager of the Mountain House Community Services District, and Dwane Milnes, the district’s financial advisor.

Milnes has started to scrutinize utility bill records and found that ECO Resources claims that nearly half of all homes in Mountain House have bills that are 30 or more days overdue. For most cities, the rate is closer to 10 percent of all customers, Milnes said.

But people told Sensibaugh and Milnes that they send in their checks 10 or more days before the due date and still get hit with late fees.

“My personal experience is I call and talk to them about billing issues and there’s no recourse and no proof it was paid on time,” said resident Jim Lamb, who had asked Sensibaugh to set up Thursday’s meeting with homeowners.

Milnes explained that checks go to a Wells Fargo lock-box service in San Francisco. The checks are recorded into electronic files, which are sent to the ECO Resources office in Sugar Land, Texas, near Houston.

Where exactly the accounting errors occur is still unclear, but the district recently hired a billing coordinator, Mary Olivarez, to track down discrepancies.

“What we have is a process problem,” Milnes said. “What I’m trying to uncover is who is not doing what, and how do I seamlessly get the information from A to B.”

Milnes said Wells Fargo is supposed to record the date it receives those checks, then relay that information to ECO Resources and credit the money to the Mountain House CSD bank account.

Some residents have taken to paying bills in person at the CSD office to get a receipt to prove they paid their bills on time — and possibly get refunds later.

“The only way to not have that late charge is to have that piece of paper,” Lamb said.

ECO Resources is under contract to operate some of Mountain House’s utilities, including water, sewer and storm drains until May 2008. Within the next year, ECO Resources must come up with a new proposal for management of the town’s utilities. The CSD could also consider competing proposals from other utility management companies.