An electrical issue with a water heater sparked the fire, Boise Fire Department spokeswoman Tammy Barry said.
Boise firefighters spent Tuesday evening battling a two-alarm fire on South Pond Street near Targee Street, and all occupants were safely evacuated, the fire department reports.
The fourplex was judged a total loss, with two adjoining apartments seriously burned and one other unit sustaining minor damage, Barry said.
The two-alarm fire was reported at 6:08 p.m. The Boise Fire Department's burnout fund and the Idaho Red Cross were available to help displaced residents,