Veronica Tate knew from the stench that sewage was among the 8 feet of water that swamped the basement of her ranch-style home after the nearby Meramec River overflowed. The larger concern for residents of her suburban St. Louis neighborhood is the unknown of what else the noxious blend might have contained.

"It came up through the sewers, I guess," Tate, a customer service representative for an insurance company, said of last week's flooding. "When you get down there and look at it, there's a smell. There's an odor."

Wastewater was a certainty in her Arnold neighborhood, given that two nearby treatment plants failed when the Meramec flooded in record fashion after days of unrelenting rain. The inundation has spewed tens of millions of gallons of untreated human waste, according to the sewer district's website, on a path toward the Mississippi River and an unavoidable southward trek to the Gulf of Mexico. Those plants remained offline Tuesday.

But the floodwaters also could include such things as fertilizers, pesticides and herbicides washed away from farmland, not to mention livestock waste, industrial chemicals, dead animals, fuel from convenience stores and toxins from railroad tracks. Even pollutants from things as small as the gas can in a flooded garage.

"You certainly don't want to expose bare skin to an unknown cocktail of chemicals," said Chris Whitley, a regional U.S. Environmental Protection Agency spokesman in Lenexa, Kansas. "We recognize it's a balancing act between the desire to have things normal again versus sitting around waiting for the water to go down or other things to happen to clean up your property. The (health) consequences posed by these other hazards can be much longer lasting."

Much of the pollution eases its way into the Meramec and other rivers that feed into the Mississippi, for many communities the source of drinking water.

By Tuesday, the inundation from last week's flooding had been cleared from Tate's home, and the 55-year-old woman's basement soon will be gutted to eliminate another potential health concern — dangerous mold that can infest soaked sheet rock, flooring and furniture. There's not yet an official tally of homes and businesses in the area that sustained damage, though Missouri Gov. Jay Nixon said Tuesday the flooding affected about 7,100 buildings in four St. Louis-area counties alone. An estimated half-million tons of debris needs to be removed, he added.

Even soggy sandbags, touted as last-ditch defenders against floodwaters, can't be kept for reuse because the inundations turn them into mountains of smelly, polluted sacks ultimately destined for landfills, along with flood-ruined household wares like sodden flooring, furniture and appliances. Well over a million sandbags were put to use in Missouri and Illinois since Christmas Day, according to governmental figures.

With each bout of broad flooding, such pollution threatens to sicken anyone who wades into the water, prompting health officials to urge affected residents — and even reporters — to proactively keep current on tetanus shots if they're unable to stay away from direct contact with the floodwaters.

Floodwaters may contain more than 100 types of disease-causing bacteria, according to a 2012 report by the Union of Concerned Scientists. And while the frequency of waterborne illnesses due to flooding is not immediately clear, the Centers for Disease Control and Prevention warns that direct contact with inundations and the fecal bacteria in them could cause gastrointestinal illness or other infections.

"The best way to avoid problems is to stay out of the water completely unless you have to be in them," Whitley said. "Let the water go down, then do your recovery. It's safer all around."

In Chester, Illinois, 60 miles southeast of St. Louis, the Mississippi rolling by is the 8,600-resident city's sole supplier of drinking water, Chester water plant supervisor Tim Crow said Tuesday. During inundations that could impact Chester, Crow said he relies on guidance from the Illinois Environmental Protection Agency.

But Crow insists the city's water supply remains safe and exceeds state environmental standards, noting that sewage in the engorged Mississippi "is so diluted when it gets to us."

"We monitor it, but at this time there's no level of concern," he said at the water plant, which treats roughly 1.5 million gallons of water a day during the winter.

The rains that caused this winter's flood, blamed already for at least 25 deaths in Missouri and Illinois and damage to hundreds of homes and businesses, ended a week ago. But the water continued rising Tuesday in southern Missouri and Illinois. Several other states along the Mississippi still were bracing for the crest.