The flood water is very likely to be contaminated with sewage and chemicals, amongst other things, which poses a health risk for those that have to wade through it to get to safety or to return to their homes or businesses.
Infections like Giardia, Salmonella, and E. coli are likely to be on the rise. If you end up ingesting any of the water, head to the doctor if you start to feel ill to rule out having any of those.
Wading around in the dirty water and dealing with demolished buildings typically don’t mix well. It’s going to be easy to get injured on rusty nails and other debris, and if those wounds are exposed to some of that previously mentioned dirty water, you could be in trouble.
If you’re in one of the affected areas and get injured, it’s important to visit a doctor, even for injuries you might otherwise just put a Band-Aid on and move on. Wounds are much more likely to get infected in situations like this, and you might need antibiotics to kill an infection before it gets out of control.
Whenever there’s warm weather and standing water, there are mosquitos. The Texas area is likely to see a few more mosquitos than they’re used to following the storm, and those mosquitos could be carrying illnesses.
After Katrina, West Nile causes doubled in the parts of Louisiana and Mississippi where the hurricane hit. That might happen in Texas as well. If you go out in the area wear bug spray, and if you do get bit be on the lookout for symptoms of things like West Nile and Zika.