(CNN) Hurricane Harvey and its aftermath have dumped trillions of gallons of rain across Texas and Louisiana over six days. Homes, office buildings and other structures along the Gulf Coast and in Houston's Harris County, were flooded, their occupants forced to find higher ground. To reach safety, most local residents waded through the murky streams, in some cases for hours.

Scientists, including Lane Voorhies, a senior environmental scientist at A&B Labs in Houston, expressed concern about what this water might contain.

"The potential for contamination is everywhere," Voorhies told Elizabeth Cohen, CNN senior medical correspondent. In particular, he worried about the health effects among people who had spent time in the water, especially those who might have gotten cut while walking through the murky depths. People with underlying illnesses, pregnant women, the elderly and young children would also be more susceptible to illnesses resulting from contact with contaminated water.

Based on sampling he'd done during previous flooding events, Voorhies took three samples on Thursday of floodwaters from different locations in Houston, though all in close proximity. He sent the samples to A&B Environmental Services, Inc. to be laboratory tested for sewage-related bacteria, chemicals and heavy metals, including arsenic, lead, mercury, cadmium, chromium and silver.

On Friday, Senthilkumar Sevukan, lab manager and microbiologist at A&B Lab, delivered the results.

Coliform and E. Coli

The total coliform samples were "huge," said Sevukan, compared to EPA standards. Coliform bacteria is present in the feces of all warm-blooded animals and humans.

The three water samples for total coliform bacteria were 57,000 CFUs, 43,000 CFUs and 45,000 CFUs. (Colony-forming units, or CFUs, estimate the number of bacteria or fungal cells that have the ability to multiply in a sample.)

Hearing these numbers, Wilma Subra, president of the Subra Company, an environmental consulting firm, audibly gasped.

"First of all, the drinking water for coliform should be non-detect and here you have these very, very elevated levels," she said. "These levels indicate the potential for sewer plant malfunction or sewer plant continuing to discharge untreated or partially treated waste."

Along with the coliform analysis, Sevukan had three sample test results for E. coli, which is part of the total coliform number: 8,600 CFUs, 3,700 CFUs and 6,300 CFUs. The EPA drinking water standard for E. coli is zero and, according to EPA criteria published in 2012 , the recreational water quality standard ranges from 100 to 410 CFUs.

"If total coliform and E. coli is high, there's a definite mixture of sewage in the water," said Sevukan. Neither bacteria is life-threatening.

The E. coli numbers did not make Subra gasp, though she noted they were "very high numbers" as well.

"E. coli causes a lot of intestinal disruption, a lot of medical conditions," she said. When you're in the floodwaters, she explained, it gets on your skin and then you touch your face, it gets in your mouth, she said, "So you can actually be inhaling and consuming it as well as skin contact."

"If you have a cut, it can enter your tissue and potentially your blood stream as well," said Subra. First-responders and people rescued from the floodwaters can become contaminated, she said, and the result could be "infections, boils and things like that on your body."

Sevukan delivered some positive news: All the heavy metal tests were below the standard EPA limits.

However, Subra greeted this news with skepticism. "After (hurricanes) Katrina and Rita, we had huge storm surge that brought in sediment sludge from the bottom of all the water bodies," she said, recalling that in some cases "it was inches to feet thick this sediment sludge."

"Because historically people just disposed of things in water bodies," said Subra, the sludge "had a lot of heavy metals in it."

Once again, in the aftermath of Hurricane Harvey, people are wading through water but you don't know if sediment sludge, contaminated with heavy metals, lies beneath it, said Subra.

What to do

Whether you are a responder or a person rescued, Subra said you need to "take a bath or shower with an antibacterial soap as soon as possible after coming out of that water." This will protect your body from continued exposure. You also need to get rid of the clothes you had on because just washing them will not destroy the harmful bacteria, said Subra.

If you come down with a boil or an infection on your legs or arms, when you see a doctor you "should emphasize to the doctor that (you) were in the floodwaters with sewage organisms in the water," said Subra. This is important so that your doctor might make a decision to treat you with medication that effectively destroys organisms such as E. coli and coliform.

Austin-based Jennifer Walker, the water resources program manager at Sierra Club Lone Star Chapter, took time away from putting together evacuee kits with her sister to speak about what's to come.

"Once the search and rescue is over, once they've explored the area and the floodwaters have receded, one of the things we actually really need to do is go out and figure out what we're dealing with," said Walker.

This includes thinking of all the different possibilities for "these chemicals and noxious things that are in pockets all over the Texas coast," she said. "Where they went and where they could possibly land. We want to make sure our communities and our children are going to be safe."

In parts of the city where there's a higher concentration of chemical plants and refineries, there's "obviously" a higher chance of contamination, said Walker. "But there are pipelines and conduits to move these substances all over Texas, frankly, but definitely on the Gulf Coast."

"The obvious places to look would be around these chemical plants and the refineries," said Walker. "But also the places where they use these chemicals. Paint and body shops, definitely, print shops, gas stations -- they have tanks of gasoline underground, huge tanks of it -- we always hear about dry cleaners, of course," said Walker.

"Those kinds of businesses are all over the place," said Walker, who noted that they also "have stringent rules in place for how they deal with and contain their chemicals -- but this is a highly unusual situation."

"My own father owns an auto repair place," she said, adding that his business had containment systems, such as a retaining wall built around the containers holding antifreeze and other chemicals around it.

While there are different kinds of controls in place, "you also don't expect 50 inches of rain and massive flooding," said Walker.

What remains behind

Natural processes -- including sunlight, oxygen and soil -- will break some of the harmful organisms down, but testing is still needed.

"We need to know what we're dealing with so we can know this stuff is going to break down in a month," said Walker. "This stuff is going to be here for a long time and we need to put some barricades around it."

"A lot of this is going to wash out into Galveston Bay and into our bays and estuaries where there's incredible commercial and recreational fishery," she said. "It's not just people. There's going to be a lot of wildlife impacted by this when all this stuff sweeps out into our bays and into Mexico."

Sierra Club created a map to catalog a lot of the potential sources, said Walker. "That was us trying to wrap our arms around this problem and also trying to get this information to the public."

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"I hope that we're able to watch it and see what happens and be proactive and get some different testing done and see what we're dealing with," said Walker. "We don't want to find out 10 years later that there is a problem and there was something we could have done."