Story highlights Elisa Lam was last seen January 31

Her parents called to report her missing February 6

The covered water tank was one of four on top of the roof and was behind a locked door

Guests said black water could come out of tap for a few seconds, then run clear

A 21-year-old woman whose body was found in a water tank of a Los Angeles hotel in February was the victim of an accidental drowning, medical examiners reported Thursday.

The decomposing body of Elisa Lam floated inside a water tank on the roof of the Cecil Hotel while guests brushed their teeth, bathed and drank water from it for as long as 19 days. A maintenance worker, checking on complaints about the hotel's water, found the Canadian tourist inside one of four water cisterns.

Tests conducted by the city Health Department found no harmful bacteria in the tank or the pipes, which had to be drained, flushed and sanitized after the discovery.

Los Angeles robbery-homicide detectives had treated the case as a suspicious death, since falling into a covered water tank behind a locked door on top of a roof would be an unusual accident, Los Angeles Police Sgt. Rudy Lopez said in February.

Lam checked into the Cecil Hotel on January 26, on her way to Santa Cruz, California, according to police in her hometown of Vancouver, British Columbia.

Five days later, she was seen on a security camera video walking into the elevator, pushing the buttons for four floors and then peering out of the opened elevator door as if she is hiding or looking for someone.

Clad in a red hoodie, Lam at one point walks out of the elevator before returning to it, pushing the buttons again. She then stands outside the open elevator doorway, motioning with her hands, before apparently walking away. It was the last day Lam was seen.

Lam's parents reported the University of British Columbia student missing in early February. Her daily calls home stopped on January 31, police told reporters on February 6 at a Los Angeles news conference.

Strange things began happening with the hotel's water supply later in the month, according to Sabina and Michael Baugh, a British couple who spent eight days there. The water pressure dropped to a trickle at times.

"The shower was awful," Sabina Baugh said. "When you turned the tap on, the water was coming black first for two seconds and then it was going back to normal."

The tap water "tasted horrible," Baugh said. "It had a very funny, sweety, disgusting taste. It's a very strange taste. I can barely describe it."

But for a week, they never complained. "We never thought anything of it," she said. "We thought it was just the way it was here."

Two former guests, Steven and Gloria Cott, filed a class-action lawsuit against the hotel in late February.

The lawsuit claims the hotel effectively failed to meet its obligation to provide proper water.

"Instead, the defendants provided water that had been contaminated by human remains and was not fit for human ingestion or to use to wash," the lawsuit states, claiming the Cotts believe that water was "tainted."