Anderson said she was still in the family's van in the driveway when husband Wayne Anderson came out and broke the news.
"I've never seen something like this in my life," said Anderson, surveying the damage to the first floor and basement by the fast-dimming daylight. Much of the ceiling above the living room and parts of the dining room had collapsed into wet, soggy piles of debris.
The family had been living in the house about three years and much of the furniture was "almost brand-new," she said.
The toilet valve apparently had not shut off when the last person went to the bathroom before leaving the house, said Battalion Chief Ronald Horn of the Hagerstown Fire Department.
The toilet water kept running, overflowing water onto the floor and saturating the insulation between it and the first-floor ceiling to the point where parts of the ceiling collapsed, Horn said.
The water penetrated to the basement, warping the home's wood floors and soaking its furnishings, he said.
The Andersons called the fire department as soon as they discovered the damage, Horn said.
The family was lucky that the house didn't catch on fire, said Horn, who said drywall had fallen on top of the cable converter box and turned the television on.
Firefighters turned off water, gas and electricity to the house and assessed the damage, he said.
Meanwhile, fire police blocked traffic past the house.
Horn said he called in the city building inspector to determine if the house is structurally sound.
"It's structurally sound, but it's going to need a lot of work," Horn said.
The couple has homeowner's insurance, he said.