It’s all got to go somewhere.

Charleston Water System says the Plum Island sewage treatment plant could run out of room for the region’s waste in about 20 years, so the utility plans to buy up every house in a nearby James Island neighborhood to lay the groundwork for expansion.

Several homes on Harbor View Circle have already been purchased by Charleston Water System, which paid more than $2.1 million for three marshfront houses in December.

This week the remaining 20 or so homeowners will get letters telling them Charleston Water System wants to buy their properties as well, sometime during the next two decades when they are ready to sell.

The utility plans to offer them an incentive to give the Charleston Water System the first option to buy.

“I would take it,” said Charleston Water System CEO Kin Hill. “If someone knocked on my door and said they’d buy my house any time in the next 20 years, for appraised value, with no commissions, and here’s a check.”

Marsha Farrior, a homeowner on Harbor View Circle, said she’ll be interested to hear the details. She has been trying to sell her home there for three years.

“I think it sounds like a great deal,” she said. “I think it’s a good idea anyway, because the residents and the water company tend to butt heads, and I think we get in each other’s way.”

Harbor View Circle is located off Harbor View Road near the James Island connector. Trucks headed for the sewage plant on Plum Island currently pass through the neighborhood to get to a causeway, and a noisy pumping station is located there as well.

Bill Carson, another resident, said he was surprised to hear about the water system’s plan.

“We would hate to have to leave here, because it’s so convenient to downtown, and it’s a great neighborhood,” said Carson, who described the community as a quiet place where everyone knows their neighbors.

“But if it’s going to be 20 years, well, that’s insignificant to me,” he said, noting that he is 79 years old.

Hill said the utility will likely rent the houses it buys, until it needs them. The Charleston Water System is already a landlord on Harbor View Circle, where it is leasing the first three houses it purchased from the prior owners.

Those homeowners had been involved in a legal challenge to the utility’s plan to run a 48-inch sewage pipe across the marsh on pilings, as part of a $186 million project to replace the area’s network of sewage tunnels. The enormous pipe is the last leg of a network that delivers the sewage of roughly 150,000 people to the Plum Island treatment plant.

After delaying the project for two years, Hill said, the challenge was dropped after the water system bought the three homes. He said the utility paid market prices plus “an additional monetary consideration.”

Despite the litigation, Charleston Water System had not let the homeowners know earlier about the plan to buy all their properties — a plan proposed to the utility in a 2007 engineering study.

“I guess it was never totally divulged that that’s what the long-term plan was,” Hill said.

Population growth in the Charleston area is driving the need to eventually expand the treatment plant, which serves the Charleston peninsula, Daniel Island, and areas west of the Ashley River.

Hill said engineering studies concluded that expanding near Plum Island was the most cost-effective and environmentally responsible option. The second choice, he said, was building a treatment plant on Johns Island.

“We could actually double the (sewage) flow again before we need any property, but we think it’s our obligation, as properties become available, to do everything we can to acquire it as amicably as possible,” said Hill. “The good news is, we don’t really need any of the property for 20 years.”