They say oil and water don't mix, but with gasoline prices rising, some swindlers are trying to get away with just water in the gas tank.

A U-Haul in the Little Rock, Ark., told FOX16 that people have been topping off the rental vehicles with water instead of gasoline before returning them — saving themselves money but wreaking havoc on the vehicles.

“They pull up, they drop it off and we don't know anything right off," General Manager Donna Nix told the station.

It's not until the truck doesn't start that employees know something's wrong, according to FOX16, and with a tank full of water, the damage to the trucks is costing the company hundreds of dollars per vehicle.

"I really look for it to get worse as fuel prices go up," Nix said.

Click here for the report from FOX16.