Texas Health and Human Secretary Dr Tom Price declared a public health emergency on Sunday after flood waters created opened up a slew of hazards.
As well as the more immediate risks of drowning or being trapped without food, floodwater brings a very real threat of infection, disease and dangerous vermin.
These are some of the threats posed by the still-rising water levels throughout the state.
Water-borne infections and diseases
While the rain might be clean, what it dredges up from the sewers and around the area is not.
Floodwater can contain harmful sewage, chemicals and waterborne germs that can cause infections and diseases for people.
People in Texas could in turn get viruses from ingesting the water or food that has been in contact with the floodwater, which would cause symptoms such as diarrhea and vomiting.
Use of hand sanitizers and purified water at shelters is recommended by officials.
Objects that have been submerged in water can also cause infection if touched or used after.
The Centers for Disease Control and Prevention recommends parents to throw out toys for children that were in the rain water unless they are thoroughly cleaned.
Trench food – which causes skin to itch, swell up, blister and peel off – is also possible after extended exposure to dirty water.
Infected wounds
Floodwater can be dangerous for people with open wounds, particularly if they have other health conditions.
Sharp objects hidden in the water could create cuts that then become filled with water-borne bacteria, causing infections.
And the harmful bacteria dredged up from the sewers and other unsanitary locations could require strong antibiotics than usual.
People with open wounds are advised to keep them clean, wrapped and away from any of the dirty water.
It’s also advised that everyone get a tetanus shot, as glass, metal and other debris could lead to the life-threatening illness.
Mosquito infections
The pools of stagnant, warm water left after the hurricane ends will be a perfect breeding ground for mosquitoes – which can then spread infections.
Zika and West Nile were among the diseases that saw increases in areas of Louisiana and Mississippi after Hurricane Katrina.
Poor people are particularly at risk as they don’t have the air conditioning and screens that can filter out the parasitic insects.
Continuous use of insect repellent is recommended to avoid infection.
Mold and cleanup concerns
The use of generators to power homes can lead to carbon monoxide poisoning, experts warn.
‘Any sort of roof over a generator is actually a problem,’ the CDC’s Renee Funk said, adding that battery-operated generators are a better alternative.
‘When people go in and out to refill the [covered petrol] generator they can be overcome,’ she explained. ‘If a structure is attached to the house, the house can fill with fumes.’
Mold is also a health hazard, the CDC warns, and all drywall and insulation tainted by floodwater or sewage should be removed from homes.
Mattresses, pillows, carpeting – even stuffed toys – should be tossed out. Hard surfaces can be disinfected with a solution of one cup of bleach to five gallons of water.
If mold covers more than 100 square feet, a trained mold remover should be sought out, experts say.
Mental health concerns
As many as 10 per cent of those who survived Katrina were left with post-traumatic stress disorder (PTSD), said Dr Pierre Buekens, Dean of Tulane University’s School of Public Health and Tropical Medicine.
That was likely to also happen in Houston, he said – thought he said most people were resilient and would get through it.
People who have strong bonds with friends and family tend to recover easier from PTSD after a natural disaster because they have a support system.
Counseling is recommended for people with lingering mental illness concerns after the natural disaster.