An arrest in the fire was announced about 10 p.m. Wednesday. Fire officials said the suspect was cooperating with investigators.
The blaze burned about 179 acres and was 75 percent contained as of 9:15 p.m., fire officials reported. Crews were working around the perimeter toward the center of the burn area, said Tooele County Fire Warden Tom Wilson.
Eight homes had been evacuated, Wilson said, and while residents were being allowed back in to check on their animals, the evacuations will not be lifted.
"There's way to much heat that hasn't been checked to allow people to spend the night," Wilson said.
The fire damaged three homes, though they were still habitable, said Willden. Three outbuildings were destroyed, including the water tank.
The water tank, which provides half of Stockton's water supply, is a "total loss," said Mayor Mark Whitney.
The roof had burned and 500,000 gallons of culinary water still inside the tank have been contaminated, he said.
Whitney said the water eventually will be shut down for at least 24 hours. When water service is back online, there will likely be restrictions. There is another water tank to the east of town.
Whitney didn't know how long the restrictions might last.
"I hate to guess," he said.
He expected the roof would have to be rebuilt on the damaged water tank, which is 100 years old.
Though residents have been ordered not to use culinary water, the lines remained open Wednesday in case firefighters need the water to fight the blaze. Strong winds have been pushing the fire away from town.
"If there's a sudden wind shift, they're going to need this," Whitney said, gesturing toward the tank.
Wilson expected the crews to stay all night, and anticipated seeing some flareups in the burn area.
The county urged people to stay out of the area.
Evacuees were able to go to a Red Cross shelter set up at the Church of Jesus Christ of Latter-day Saints at 253 S. 200 East in Tooele, according to Tooele County Emergency Management.
Up to 50 firefighters, two air tankers and helicopters were fighting the fire.
In 1975, a Stockton wildfire killed sheriff's Sgt. Lauren Dow and Tooele City Animal Control Officer Danny James. "[They] were driving a vehicle near the 300-acre blaze when winds abruptly pushed the flames in their direction," according to the Utah Law Enforcement Memorial.