“We haven’t seen large-scale private investment in infrastructure like this,” Professor Kaiser said. “Lake Columbia is really an unprecedented development.” (Texas A&M University is a corporate sponsor of The Texas Tribune.)

The Lake Columbia partnership and other forays by the private sector into municipal water development come as cities’ water supplies, and financing, are running dry.

“The fiscal condition the country is in, down to municipality X, Y and Z, makes it very difficult for traditional funding to happen,” said Bill West, general manager of the Guadalupe-Blanco River Authority, a water district based in Seguin. “There’s no way for the state to finance all the water infrastructure it needs.”

The river authority is considering its own public-private partnership for a plant along the gulf coast that would desalinate seawater and produce power. The Brazos River Authority and the City of Odessa are two examples of public entities interested in similar partnerships to build plants to desalinate either brackish groundwater or seawater. The expense of developing these new water sources — often hundreds of millions of dollars — makes local utilities eager for private capital. The private groups, for their part, are interested in profits and also in the water.

Kelley Holcomb, general manager for the Angelina & Neches River Authority, said that tight budgets made navigating expensive and lengthy permit processes for a reservoir impossible under traditional financing arrangements. Mr. Holcomb added that a final administrative step for the Lake Columbia project — a permit from the Army Corps of Engineers — could cost up to $13 million. “Local folks just don’t have the cash for that,” he said.

But the high costs can also be a barrier for private firms. Professor Kaiser said that even as private entities known as water marketers rush to sell groundwater to cities, public entities still typically build the expensive pipelines that carry the water.

Private water groups have long occupied another niche in Texas: selling water to rural communities. Recently, those companies have come under scrutiny from the Legislature for their rates. David Burghard, a Hays County resident, told a legislative committee last month that his water rates rose more than 200 percent in February and that he was concerned there would be “no limits.” The private companies counter that they are pouring millions of dollars into upgrading water infrastructure.