Floodwater While Travelling: The Hidden Health Risks You Might Miss

Leptospirosis, melioidosis, ruined medication and contaminated water systems kill people every year after floods. Here is what travellers need to know before the water rises.

What a flood actually does to your health

Floods kill more people every year than most other natural disasters, and most of those deaths are not from drowning. Flash floods account for approximately 85% of all flooding cases worldwide, and the health risks they generate last weeks or months after the water recedes. For travellers, the threat is compounded by unfamiliar surroundings, disrupted pharmacies, and a body that has not built up local immunity to the pathogens that floods push into waterways.^[1]

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult your doctor or a travel medicine specialist before travelling to flood-prone regions, especially if you have a pre-existing condition or take regular medication.

The waterborne disease risk is real, and it starts fast

Floodwater is not just water. It carries sewage, agricultural run-off, industrial waste, and the urine of rodents displaced by rising water. Flooding was consistently associated with increased incidence of leptospirosis, cholera, hepatitis A, and dengue across a systematic review of 71 studies published in BMC Infectious Diseases in 2026.^[2]

Leptospirosis deserves particular attention. Leptospirosis risk often increases after a hurricane or flood when people have contact with contaminated water or soil, according to the CDC. Without treatment, it can progress to kidney failure, liver failure, and meningitis. The incubation period is two days to four weeks, meaning you may not feel ill until you are home.^[3]

The 2024 floods in Rio Grande do Sul, Brazil, illustrate the scale. In the weeks following those floods, 7,818 confirmed cases of leptospirosis were reported, alongside ten outbreaks of diarrhoeal diseases. Travellers in flood-affected areas face the same pathogen exposure as residents, without the local immunity or the familiarity with early symptoms.^[4]

Melioidosis: the infection most travellers have never heard of

Melioidosis is caused by the bacterium Burkholderia pseudomallei, which is found in soil and becomes a serious health risk after heavy rain or flooding. The bacteria live deep in clay soil and are brought to the surface when floodwater churns the ground. Travellers wade through it. They touch contaminated mud during post-flood sightseeing or volunteer clean-up. They may not feel ill for weeks.^[5]

Queensland, Australia, recorded 94 cases of melioidosis in the first seven weeks of 2025, more than three times the number for the same period in 2024. There were 12 deaths, with almost all cases linked to flooded areas. The death rate for melioidosis in Australia is 10 to 20 percent even with prompt hospital care. In parts of Southeast Asia, where treatment access is limited, it reaches 40 percent.^[6]

The disease is endemic to northern Australia and Southeast Asia. Melioidosis cases may increase after hurricanes, heavy rain, and other severe weather events, and the CDC specifically advises clinicians to consider it in any patient who has recently waded through floodwater in an endemic area. A presentation mimicking flu or pneumonia within three weeks of flood exposure warrants investigation.^[7]

Wound infections and tetanus: the cut you didn't notice

Floodwater carries debris, glass, rusted metal, and broken wood. Tetanus can enter the body via cuts or puncture wounds exposed to contaminated water or debris. A minor graze that goes unnoticed in the chaos of a flood evacuation becomes an infection risk. Check your tetanus vaccination status before you travel, not after.^[8]

Any open wound that contacts floodwater needs immediate cleaning with clean water and antiseptic. Cover it with a waterproof dressing and seek medical assessment if redness, swelling, or discharge appears within 48 hours. In flood-affected areas where hospital access is disrupted, this timeline matters.

Your medication is at risk too

Flooded rooms destroy medications in ways that are not always visible. The US FDA advises that drugs should be discarded if they came into contact with flood or contaminated water, even in sealed original containers. Contamination penetrates screw-top lids, snap caps, and dropper bottles. A tablet that looks intact after flood exposure may carry pathogens that cause serious illness.^[9]

Temperature-sensitive medications face a second threat. Power outages after floods interrupt refrigeration. Insulin that is not refrigerated loses potency faster than the labelled expiration date. Any injectable biologic or refrigerated medication in your bag requires a cold-chain plan that does not depend on mains electricity. An insulated pouch with ice packs buys roughly 24 to 48 hours. After that, replace the supply.^[9]

The access problem compounds the storage problem. Flooded roads cut pharmacy supply chains. A medication that was readily available before the flood may be out of stock for days or weeks. Carry a digital copy of your prescription and a summary of your medical history. A cold-chain medication that needs refrigeration is particularly vulnerable when a flood disrupts infrastructure.

Drinking water becomes dangerous before you realise it

Water treatment plants are often built next to rivers, making them among the first facilities to be compromised when flood levels rise. Water treatment and distribution systems are particularly vulnerable when flooding occurs, according to Johns Hopkins Bloomberg School of Public Health. Tap water in a flooded city may look normal while carrying hepatitis A virus, norovirus, Campylobacter, and pathogenic E. coli.^[10]

Sewage overflow caused by flooding increases the risk of infectious disease, particularly gastrointestinal infections like traveller's diarrhoea. Floods increase the risk of viral infections such as norovirus, hepatitis A and rotavirus, as well as bacterial infections due to Campylobacter and Salmonella. Use bottled water for drinking and tooth-brushing until authorities confirm the tap supply is safe. If bottled water is unavailable, boil water for at least one minute before using it.^[11]

The post-flood disease risk extends well beyond the flood zone

Standing water after a flood breeds mosquitoes within days. In Spain, the October 2024 Valencia flash flood brought bacteria, viruses, protozoa, and insect vectors into the same inundated zone. Environmental samples collected in the Valencia flood zone identified viruses, bacteria, protozoans, helminths, insect vectors and snail vectors. The health risk from that single event persisted for months.^[12]

Research published in Nature Water in 2025 found that post-flood hospitalisation risks persist for months, varying by flood severity, age, and population density. If you were in a flood-affected area and develop unexplained fever, diarrhoea, respiratory symptoms, or wound complications in the weeks after returning, tell your doctor about the flood exposure. It changes the differential diagnosis.^[13]

What to do before, during, and after a flood as a traveller

Pack a waterproof medication bag. Store all medications in a hard-sided waterproof case or sealed zip-lock bags inside your luggage. Even brief submersion can contaminate a prescription supply through packaging that appears intact.

Carry your medical records digitally. A travel insurance policy that covers natural disasters is only useful if local doctors can see your diagnoses and medication list quickly. Store your International Patient Summary on Nomedic so it is accessible from any device, in any language, even if your paper documents are destroyed.

Check your vaccination status before departure. Hepatitis A and tetanus are both directly relevant to flood exposure. Both are preventable. Confirm they are current at a travel clinic at least four weeks before travel to flood-prone regions. To learn more about other travel-recommended and routine vaccines, read our travel vaccination checklist.

Avoid wading unless unavoidable. If you must enter floodwater, cover all open wounds with waterproof dressings before contact. Waterproof boots and gloves are not excessive caution; they are the difference between exposure and no exposure to leptospirosis, melioidosis, and wound pathogens.

Boil or use bottled water immediately after any flood event. Do not rely on the tap even if it flows normally. Municipal systems can be contaminated hours before a boil advisory is issued. Use bottled or boiled water for drinking, tooth-brushing, and taking oral medications.

Monitor for symptoms for up to four weeks after exposure. Leptospirosis has an incubation period of two to four weeks. Melioidosis can incubate for up to 21 days and, rarely, lie dormant far longer. If you develop fever, headache, muscle aches, or respiratory symptoms after flood exposure, seek medical care and mention the exposure explicitly. Check the relevant travel health advisory for your destination before you depart. Nomedic's city guides also provide information on destination-specific health risks.

The 2024 and 2025 flood season raised the baseline risk

In 2024, approximately a third of Europe's river systems experienced high flood levels, the most widespread flooding on that continent in a decade. Flooding has occurred in 50 of the 53 countries of the WHO European Region during the past two decades. The 2024 Valencia flood in Spain killed at least 220 people. It is no longer a fringe risk for travellers in Europe, let alone in Asia or South America.^[14]

A 2025 NIEHS-funded study published in Nature Medicine found that flooding events are associated with increased death rates for cardiovascular diseases, infectious diseases, injuries, and respiratory diseases. These are not niche outcomes. They affect ordinary travellers who get caught in flash floods while in a destination city.^[15]

The practical response is not to avoid travel to flood-prone destinations. It is to travel prepared: vaccinated, with medications stored safely, medical records accessible, and enough knowledge to recognise symptoms and seek care promptly.

Frequently asked questions

Can you get leptospirosis from wading through floodwater as a tourist?

Yes. Leptospirosis is transmitted through contact with water or soil contaminated by infected animal urine, and flood events significantly raise exposure risk. The CDC confirms the risk increases after floods, and the incubation period is two days to four weeks, meaning symptoms may not appear until after you have returned home. If you develop fever, headache, or muscle aches after flood exposure, tell your doctor immediately.

What diseases are most common after floods in Southeast Asia and Australia?

Leptospirosis and melioidosis are the two infections most specifically linked to flood events in northern Australia and Southeast Asia. Waterborne diseases including hepatitis A, cholera, and typhoid fever also increase after floods disrupt water treatment systems. Queensland recorded 94 melioidosis cases with 12 deaths in the first seven weeks of 2025, following widespread flooding.

Is it safe to use tap water to take my medication after a flood?

No. The US FDA advises using bottled or boiled water to take oral medications whenever a boil water advisory is in effect. Water treatment plants are among the first facilities disrupted by flooding, and tap water may be contaminated before any advisory is issued. Use only sealed bottled water or water you have boiled and allowed to cool.

What happens to prescription medication that gets wet in a flood?

The FDA recommends discarding any medication that has contacted floodwater, even in original sealed containers with screw-top lids or snap caps. Contamination is not always visible and can cause serious health effects. Discard and seek replacement. If you are abroad, a digitally stored prescription summary gives a local doctor or pharmacist the information needed to help replace your supply.

How long after leaving a flood zone am I still at risk of getting sick?

The risk extends for weeks. Leptospirosis has a two-to-four-week incubation period. Melioidosis typically presents within 21 days of exposure but can incubate far longer in rare cases. Research published in Nature Water in 2025 found that hospitalisation risks from flood exposure persisted for up to 210 days. Report flood exposure to your doctor even if you feel well at first.

Should I get vaccinated before travelling to a flood-prone area?

Yes. Hepatitis A and tetanus are both directly relevant to flood-related risk and are vaccine-preventable. Consult a travel clinic at least four weeks before travel to flood-prone destinations to confirm these are current. There is no vaccine for leptospirosis or melioidosis, so protective clothing and avoiding floodwater contact remain the primary defences for those two infections.