FARMINGTON – It will be weeks before tenants in the Tri-County Mental Health apartment building can return there because a sprinkler sent water cascading down all three floors early Tuesday morning.

“There was a lot of water damage. Water ran through (from the third floor) all the way to the basement,” Deputy Fire Chief Tim Hardy said Tuesday. The building is at 108 Middle St. and has five apartments.

Four of the five tenants were home when a third-floor sprinkler activated, setting off an alarm just before 1 a.m., he said. They were evacuated.

The cause of the activation was “human element,” the deputy chief said Tuesday night, and the incident is being investigated.

Firefighters shut off the sprinklers about 15 minutes after arrival, Hardy said.

It will be weeks before an accurate estimate of damage is possible, he said.

“There are probably two and a half apartments that hadn’t been affected by water,” he explained. Besides the other apartments that were soaked, there is a “big common living room that was extensively damaged” and hardwood floors, he said.

Servicemaster and an electrician were beginning cleanup and repairs in the building Tuesday afternoon.

“I did talk to one tenant who verified she had renter’s insurance,” Hardy said.

The tenants will need to be out of the building for a few weeks while reconstruction is done, he said.

“They’ve all gone with family or relatives,” he said Tuesday night.

Tri-County Mental Health representatives declined comment Tuesday.

Staff editor Mary Delamater contributed to this report.