KEY LARGO -- It is dusty, inconvenient and expensive for homeowners to hook up to the new central sewer, but it has provided an economic boost for many local businesses with promises of more to come.

Plumbing companies, obviously, have been the primary beneficiary of a state mandate requiring homeowners to abandon their septic systems and connect to Key Largo's new 2.3-million-gallons-a-day sewage treatment plant.

But also reporting a steady upturn in business attributable to homes connecting to Key Largo's $155 million centralized system are general contractors, fence, landscaping and auto parts companies, hardware and plumbing supply stores and gas stations.

"We've seen about a 20 percent increase in plumbing sales this year," said Eli Manresa, manager at Keys Supply Inc. in Key Largo. "Considering the economy the past two years, this is a significant increase."

Up the highway is KLI True Value, where owner Bob Silverman says his plumbing department has seen a gradual rise in sales.

"It's been a long, slow process, not a spike but a slow crescendo," he said, referring to sales generated by contractors and plumbers who shop at his home improvement center while installing laterals.

"We're also picking up local do-it-yourselfers who spend an average of $200 on supplies," he said.

Windy Day Plumbing of Islamorada has several contracts to install lateral sewer lines in Key Largo. The company has been kept so busy that it subcontracted trenching work to general contractor John Sorensen. The uptick in jobs prompted Sorensen to hire two employees to help.

Windy Day owner Rick Prather says other merchants are benefiting in ways that might not be immediately apparent.

"I take 10 men to Mrs. Mac's every day for lunch," he said.

Jose Arrasola of the Tavernier CeMex plant says sales of pearock began to increase about a year ago as the result of contractors needing rock to cushion sewer pipes and to re-landscape yards.

Landscapers and fence companies have been called to make repairs to jobs that have been done hastily or improperly.

"We are getting calls to clean up after the plumbers," said Vicki Matthews, co-owner of Monroe County Fence.

"A lot of people have pets and they are finding that the fences are not being put back tight enough to prevent their dogs from going under the fence," she said. "Also some of the more careful local contractors are hiring us to do fence removal and replacement and it's helped a little, but we're not seeing a drastic change."

Not yet.

The Key Largo Wastewater Treatment District this month is sending certified notices to about 6,000 Key Largo homeowners informing them that they have 30 days to connect to the system before monthly service charges begin appearing on their water bills. That edict will likely trigger a last-minute rush by homeowners to find a contractor to trench through coral rock, install pipes and connect them to the sewer.

Many homeowners began connecting to the system earlier this year after the district notified them that service was available in their neighborhoods. A smaller, temporary treatment plant serving those communities has been replaced by the larger plant.

Last week, general contractor Sorensen was on his way to Atlanta to pick up a backhoe for trenching work in anticipation of the 6,000 laterals. He pointed out that the heavy equipment required for trenching generates fuel sales for local gas stations and parts sales for auto supply companies.

sgibbs@keysnews.com