Testing and cleaning North Carolina’s water supply post-Florence could prove tricky. A microbiologist explains why

Hurricane Florence dropped record-breaking amounts of rain as it hovered over the Carolinas last week. The resulting floodwaters killed dozens of people and created a lingering crisis for drinking water supplies. Across North Carolina, lagoons full of livestock waste, enclosures full of dead chickens and hogs, raw sewage from wastewater treatment plants, and coal ash ponds are all overflowing. The Environmental Protection Agency issued a statement on Monday that at least 23 drinking water systems in the state had temporarily halted their operations and that 21 others were operating with boil water advisories.

Rachel Noble, a microbiologist at The University of North Carolina in Chapel Hill, and her team are working to track potentially dangerous bacteria and viruses as they flow through North Carolina’s water system. She told Science about poststorm threats to drinking water and how to cut down on the dangerous lag time in the tests that detect them.

This interview has been edited for clarity and brevity.

Q: What are the common contaminants in flooding situations like this?

A: Bacterial pathogens like E. [Escherichia] coli, salmonella, and Campylobacter are common in floodwaters. Vibrio bacteria are naturally found in estuaries like those along the Carolina coast and could have been washed in with storm surge. There are also viral pathogens like Norovirus and adenovirus, and some less common parasites. A lot of these exist in our sewage systems, but we don’t ever come in contact with them unless there’s a breach or spill.

Q: What can happen if a person encounters these pathogens?

A: If you ingest enough of them or they come in contact with a wound, they can cause gastrointestinal illness like diarrhea, vomiting, and nausea. The sad thing about bacterial and viral pathogens is once you become infected, you can then carry that on to your family members, even if they haven’t been exposed to that particular floodwater.

Q: How do cities test for contamination after a storm?

A: Municipal systems have a regular water testing protocol, and then whenever a testing result shows there’s been contamination, the system is treated and a boil water advisory is issued in the meantime. One of the unfortunate things about our current system is that these tests can take between 1 and 2 days. So these systems in North Carolina were probably contaminated during the storm, but there’s been a lag time for us to understand the level and extent of contamination and get this information out to the public.

Q: About 900,000 households in the state rely on private wells for their water. What about them?

A: It’s going to take some time for those to all get tested. It’s a matter of getting personnel out there. Power is still out in some areas, and some areas are still being flooded and are inaccessible. To be safe, people should stick to bottled drinking water until their well can be tested.

Q: What is the process for clearing water systems of these contaminants?

A: Typically, it’s a chlorination process similar to what you would do with a swimming pool. They let that chlorine sit in the system for about 24 hours. That works well for the contaminants we’re familiar with, but I’m concerned about bacteria or chemicals that we might not understand from hog farms or other industrial waste. We don’t understand how they’re transported through water systems and we don’t understand how long they persist.

Q: Are you planning to run experiments to learn more about these contaminants?

A: Yes, my lab is already investigating what happens to these contaminants as they move through the water system to the coast. We’re also working really hard on improving some of the methods to test for these things so that we can get results in only about an hour or two.

Q: How do you design a faster test?

A: Rather than the traditional method of relying on the bacteria to grow in an incubator, we just test directly for the contaminant’s DNA in the water sample. We can get results for E. coli or for enterococcus in about 45 minutes. We are working to get these tests approved for drinking water, other types of water, and for shellfish. But getting federal agency approval can take a while.

Q: How could we better secure water systems against contamination?

A: We could improve the ways that municipal water systems are sealed or protected from flood waters. We can do a better job with processing industrial waste and hog lagoons—we just don’t have a lot of incentives to do so. There’s no money in processing hog waste at the moment.

We should be looking to improve our response to microbial and chemical contaminants before future events like Florence. These are the things that we eat and drink afterwards, and protecting them isn’t getting enough attention right now.