John Bacon

USA TODAY

An aging water treatment plant, a nasty algae in Lake Erie and weeks of dry, still weather conspired to sabotage Toledo's drinking water, experts say.

Mayor D. Michael Collins lifted the ban on drinking tap water Monday, saying tests showed the water is once again clear of the toxins that had sent more than 400,000 northwestern Ohioans scrambling for drinkable water since Saturday morning.

"Our water is safe," Collins said. "Families can return to normal life."

Collins said carbon and other chemicals were used to clean the water of toxic microcystin. Lucas County, with a population of 440,000 including Toledo, advised residents to flush hot water faucets for 15 minutes and cold for five minutes before drinking the water.

The water ban had been complicated because boiling the water, a common tool to combat contamination, only serves to make microcystin more concentrated, officials said. Stores sold out of bottled water quickly. Toledo opened a half-dozen bring-you-own-container water distribution sites. Fire stations helped out.

"We would like to thank our community for their patience and their support during this water emergency system as well as all of those who assisted during our community's moment of challenge," Collins said in a statement.

The all-clear was issued publicly at 9:29 a.m. ET. Six hours earlier, Collins announced that federal and state tests had indicated the water was fine, but city tests in two neighborhoods showed lingering, questionable levels of the toxin. Collins said he waited for more test results because he did not want to isolate those neighborhoods and because he wanted to wait until he could "put my head on a pillow and be comfortable with my decision."

Toledo's water woes were not the first involving algae in Lake Erie. Last year, about 2,000 residents of nearby Carroll Township were prohibited from drinking water from their taps for a few days because of toxins linked to the blue-green algae.

"We sit with 20% of the fresh water supply of the entire planet at our doorstep," Collins said of the Great Lakes. "If we hesitate to respect that then we are going to jeopardize this entire corridor of the United States and the future of our children."

Water treatment plants aren't required to test for microcystin under federal and state regulations. But Patrick Lawrence, a geography professor at the University of Toledo, credits Toledo with starting to test for the toxin last year amid concerns about the increasing algae growth in Lake Erie, which supplies the city water plant.

Lawrence said algae bloom has been a growing problem in the Great Lakes for years. That made Toledo ground-zero for the problem.

"Warm, shallow water is perfect for the algae," Lawrence said. "Lake Erie is the shallowest lake and the western basin (near Toledo) is the shallowest part of the lake."

The algae grows under water, floats to the surface and releases toxins at it decays. Weeks of little wind or rain exacerbated the situation, he said.

Adding charcoal to the treatment process is a short-term fix, he added. The city's 70-year-old plant needs upgrading, which could cost hundreds of millions of dollars. And there are the issues of wastewater treatment discharges, agriculture runoff and even yard fertilizers.

"We have reached a real tipping point," Lawrence said. "When it affects our drinking water, it's something you can't ignore."

Charles Haas, a professor of environmental engineering at Drexel University in Philadelphia, agreed with Lawrence that expanding the cleaning capacity of the water treatment plant and controlling the levels of phosphorous and nitrogen in Lake Erie will be key to curbing the problem. And he said the problem is a national one.

"With climate change at our heels, I think we will see more of this — and not just in Toledo," Haas said.