Washington County's population is skyrocketing, leading to projections that by 2050 — and perhaps as soon as 2035 — as many as 648,000 people will live in Utah's arid southwest.

When that happens, said Ron Thompson, director of the Washington County Water Conservation District, the county will have to supply about 210,000 acre-feet of water to serve those residents. At present, developed water supply is only 72,000 acre-feet, he said Monday during a meeting of the governor's Water Delivery Financing Task Force.

Gov. Olene Walker organized the group to devise recommendations about two big water projects, the Bear River Project and a pipeline from Lake Powell to supply Washington County, mostly St. George. (A spur pipeline to Cedar City is possible, too.)

Projections about the number of people who would be served by the Bear River Project are still being formulated and should be released soon. But amazing predictions already are on the record for booming Washington County.

"Our county has gone from just under 90,000 in 1990 to today, just under 116,000 people," Thompson said.

One steadily rising curve, the one that Thompson believes is more realistic, shows the 648,000 level by 2035; another, based on state projections, shows that many people by 2050.

Complicating the picture is that the 210,000 acre-feet projection is based on Washington County's managing to conserve an enormous amount of water. Without that conservation, according to Thompson, the need would be another 80,000 acre-feet.

Either way, the huge water demand can't be met without the pipeline, according to a chart Thompson released. It shows the lion's share of new potential water, 70,000 acre-feet, will come from a Lake Powell pipeline.

The 120-mile pipeline and its Fort Pearce Reservoir would cost $370 million in today's dollars. Assuming they would be built in 2018, and adjusting for expected inflation, Thompson said the cost at that time would be $593 million.

"The route for the pipeline essentially follows the state highway system," he said.

The problem with that is the highway not only goes through two counties, it also dips into Arizona and back to Utah.

Along the way, U.S. 89 climbs through rugged terrain called the Cock's Comb, south of Paria, Kane County. The site is 3,000 feet higher than St. George, necessitating a pumping station for the pipeline. From the Cock's Comb, the water flows downhill. Thompson expects the revenue from hydroelectric power would pay for the pipeline's operations and maintenance.

However, that doesn't cover the construction costs. Even if water users repaid most or all of the construction cost, state funding may be needed if the project is to be built.