WATERVILLE —A fire that broke out Friday in one of the Lockwood mill buildings on Water Street has been deemed accidental and caused by improperly discarded staining rags that spontaneously combusted in a construction zone, according to fire officials.

Shannon Moss, spokeswoman for the Maine Department of Public Safety, released that information in an email Monday. The state Fire Marshal’s Office had investigated the fire, along with Waterville Fire Department.

The fire was mostly contained by the building’s sprinkler system, fire officials said at the time.

Waterville firefighters responded to an alarm at the 6 Water St. building, which is being renovated into apartments, shortly before 6:30 p.m.. When they arrived, an alarm was sounding and the building’s occupants had evacuated.

In a news release issued Sunday, Deputy Waterville fire Chief Dan Brown said water was seen running between floors in the building’s northwest corner, and smoke was found in the stairwell.

A second alarm drew Winslow Fire and Rescue, and crews discovered a smoldering fire in a construction zone on the fifth floor. The building’s sprinkler system largely contained the fire and fire crews found it had not spread.

Only the third floor of the mill building is currently occupied. Because of damage caused by water and the fire protection systems being disabled, 29 occupants in 14 units were relocated Friday, with occupants of three units still displaced Monday. With the help of the Waterville Housing Authority, they were provided transportation to temporary lodging at a nearby hotel, Brown said.

The mill building, one of three in the Lockwood-Duchess Mill complex, has been undergoing renovations to convert the space into housing.