MENDOCINO COUNTY (CBS13) – Mendocino County Sheriff Tom Allman has a new mission: catching illegal marijuana growers for stealing water.

“We’re now becoming the water police,” Allman said.

He estimates thieves will use up to five million gallons of water a day in the fall — and that’s water Mendocino County simply doesn’t have.

The town of Willits – which relies almost entirely on rainfall to fill its two reservoirs – could run out of water in less than 90 days. And while people who live and work there make sacrifices to conserve, they know exactly what’s happening outside city limits.

“People will just be taking water out of the shared, you know, out of a creek or other water source so it’s having a really negative impact on our forest lands, on our streams,” said Willits Mayor Holly Madrigal.

In Calaveras County more than four hours away, one rancher told CB13 that he’s got pot growers with cartel ties living on his property – stealing water. He’s discovered a half-dozen grows on his vast land by looking for the signs.

“Yup there’s a scale in here.”

James found another grow on his property when he stumbled on an irrigation pipe the growers had buried underground, using a pond as a water source.

“They tapped the reservoir and, of course, drained all the water. So that affects me and the cattle,” James said.

Sheriff Allman says some growers tap into open irrigation canals, or even drill illegal wells. Others tap into their neighbor’s water tanks and bury the pipe. And the most flagrant, seen about four times a year:

“Somebody will take a PVC pipe and, just in front of god and everyone, just put it directly into one of the headwaters of our rivers here and pump water out of that and send it to a holding tank,” Allman said.

Allman has a message for water thieves: they will face a stiff sentence for stealing a natural resource.

“We’re going to arrest you for grand theft. It’s not petty theft, it’s grand theft of natural resources.”