Floodwater Contamination: The Most Common Diseases & How to Avoid Them
, by Tatianna Gerard, 18 min reading time
Floods are among the most devastating natural disasters, bringing destruction, displacement, and hidden health hazards. While the immediate dangers of rising waters and strong currents are well-known, the aftermath of a flood poses an equally serious threat—waterborne diseases. Contaminated floodwaters mix with sewage, chemicals, and debris, creating a breeding ground for bacteria, viruses, and parasites that can spread illness quickly through communities.
In Australia, flooding occurs in three primary forms, each with its own risks:
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Riverine floods – The most common type, caused by prolonged heavy rainfall or overflowing rivers, leading to widespread flooding across low-lying areas.
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Flash floods – Sudden, intense rainfall overwhelms drainage systems, causing rapid flooding in urban areas with little warning.
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Coastal floods – Driven by storm surges, cyclones, or rising sea levels, these floods bring seawater inland, damaging infrastructure and contaminating freshwater sources.
Regardless of the type of flooding, the aftermath presents a significant public health risk. This blog will explore the most common waterborne diseases that emerge during and after floods, including bacterial, viral, and parasitic infections, as well as fungal and other flood-related health concerns.
Bacterial infections
Floodwaters are often teeming with harmful bacteria, creating a serious health risk for anyone who comes into contact with contaminated water. As floodwaters sweep through cities, towns, and rural areas, they mix with sewage, industrial waste, and decaying organic matter, providing the perfect conditions for bacteria to thrive and spread.
Infections can occur through ingesting contaminated water, eating food exposed to floodwater, or even wading through infected waters with cuts or open wounds. The most common bacterial infections following floods include Leptospirosis, Cholera, Typhoid Fever, and Dysentery (Shigellosis)—each capable of causing severe illness if left untreated.
1. Leptospirosis
Leptospirosis, sometimes called the "floodwater disease," is one of the most frequent bacterial infections after floods. It is caused by the Leptospira bacteria, which is found in animal urine (especially from rodents, cattle, and dogs) and can spread rapidly in floodwaters.
How it spreads:
- Walking through or swimming in floodwater contaminated with infected animal urine.
- Contact with mud, soil, or surfaces exposed to contaminated water.
- Infection occurs through cuts, wounds, or even mucous membranes (eyes, nose, mouth).
Symptoms to watch for:
- Fever and chills
- Severe muscle and joint pain (especially in the calves and lower back)
- Vomiting, nausea, and diarrhoea
- Headaches and sensitivity to light
- In severe cases, kidney or liver failure, internal bleeding, and meningitis can occur, requiring urgent medical attention.
2. Cholera
Cholera, caused by the Vibrio cholerae bacteria, is a severe diarrhoeal illness that spreads rapidly in areas where clean drinking water is scarce after a flood. Contaminated water supplies can turn into a breeding ground for cholera outbreaks, especially in densely populated or poorly sanitised areas.
How it spreads:
- Drinking contaminated water.
- Consuming flood-exposed food that hasn’t been disinfected or properly cooked.
- Poor sanitation and lack of handwashing after handling contaminated materials.
Symptoms to watch for:
- Profuse, watery diarrhoea (often described as "rice-water stools").
- Severe dehydration and electrolyte imbalance.
- Vomiting and muscle cramps.
- Rapid heart rate and low blood pressure, which can lead to shock if untreated.
Cholera can cause life-threatening dehydration within hours, making immediate medical treatment and rehydration crucial.
3. Typhoid fever
Typhoid fever, caused by Salmonella Typhi bacteria, is another serious waterborne disease that spreads rapidly after floods due to contaminated drinking water and poor sanitation. Unlike cholera, which progresses quickly, typhoid fever can develop gradually, making early diagnosis critical.
How it spreads:
- Drinking or eating contaminated food or water.
- Poor hand hygiene after contact with flood-contaminated surfaces.
Symptoms to watch for:
- Prolonged high fever (lasting more than a week).
- Weakness and fatigue.
- Severe abdominal pain and bloating.
- Diarrhoea or constipation.
- Skin rashes or red spots on the chest and abdomen.
If left untreated, typhoid can cause internal bleeding or intestinal perforation, requiring emergency medical intervention.
4. Dysentery (Shigellosis)
Dysentery, also known as Shigellosis, is a severe intestinal infection caused by Shigella bacteria. Floodwaters can contaminate drinking supplies, and poor hygiene during flood recovery efforts can lead to widespread outbreaks.
How it spreads:
- Drinking contaminated water.
- Consuming flood-exposed food that hasn’t been properly disinfected.
- Direct person-to-person transmission due to poor hand hygiene.
Symptoms to watch for:
- Severe, bloody diarrhoea
- Painful stomach cramps
- High fever and chills
- Dehydration and fatigue
Shigellosis can spread quickly in flood shelters, crowded relief centres, and households without proper sanitation, leading to rapid dehydration and complications.
Viral infections
Unlike bacteria, which can often be killed with antibiotics, viruses have no direct cure—making them a serious concern in flood-affected areas. Floodwaters and poor sanitation create the perfect storm for viral outbreaks, as contaminated water sources, overcrowded shelters, and close human contact increase the risk of infection.
Viruses can spread through contaminated drinking water, flood-exposed food, or even person-to-person contact, leading to outbreaks of Hepatitis A, Norovirus, and Rotavirus. These infections can cause widespread illness, especially among vulnerable groups like children, the elderly, and those with weakened immune systems.
1. Hepatitis A
Hepatitis A is a highly contagious viral infection that affects the liver, often spreading through contaminated water and food in flood-affected regions. Once ingested, the virus travels to the liver, causing inflammation and impairing liver function.
How it spreads:
- Drinking contaminated water or consuming flood-exposed food.
- Poor sanitation—especially in overcrowded shelters or relief centres.
- Close contact with an infected person who hasn’t washed their hands properly.
Symptoms to watch for:
- Jaundice (yellowing of the skin and eyes)
- Fatigue, nausea, and loss of appetite
- Fever and stomach pain
- Dark urine and pale stools
While Hepatitis A isn’t usually fatal, it can cause severe liver damage, especially in older adults or those with pre-existing liver conditions.
💡 Prevention tip: Always boil drinking water in flood-affected areas and avoid eating raw or unwashed food. If available, getting vaccinated against Hepatitis A is highly recommended.
2. Norovirus
Nicknamed the "winter vomiting bug", Norovirus is a highly contagious virus that spreads rapidly during and after floods. It causes sudden and severe gastrointestinal illness that can be perceived as food poisoning, leading to dehydration and rapid spread in crowded conditions.
How it spreads:
- Drinking or eating contaminated food or water.
- Person-to-person transmission—the virus spreads easily through hand contact, shared surfaces, and food handling.
- Floodwaters carrying human waste or sewage contamination.
Symptoms to watch for:
- Sudden onset of vomiting and diarrhoea
- Severe stomach cramps and nausea
- Dehydration, dizziness, and weakness
- Mild fever and chills
Norovirus spreads like wildfire—once one person is infected, entire households, shelters, and workplaces can quickly experience outbreaks.
3. Rotavirus
Rotavirus is a highly contagious viral infection that primarily affects infants and young children. It is one of the leading causes of severe diarrhoea worldwide, especially in flood-affected regions where clean drinking water is scarce.
How it spreads:
- Contaminated water sources in flood-damaged communities.
- Poor hygiene and lack of proper sanitation.
- Person-to-person transmission—especially among children in close living quarters.
Symptoms to watch for:
- Severe watery diarrhoea that can last for days
- Frequent vomiting, leading to dehydration
- Fever and irritability (especially in infants)
- Loss of appetite and fatigue
Rotavirus infections can quickly lead to life-threatening dehydration, especially in young children without access to proper medical care.
💡 Prevention tip: Rotavirus vaccines are highly effective in preventing severe infections. Parents in flood-prone areas should ensure their children are vaccinated.
Parasitic infections
While bacteria and viruses can cause rapid and severe illness, parasites are another hidden danger that often emerges after floods. Unlike bacteria or viruses, parasites can survive in the body for weeks or even months, causing chronic digestive issues, fatigue, and nutrient deficiencies.
The most common parasitic infections after floods include Giardiasis, Cryptosporidiosis, and Amoebiasis—each capable of causing severe diarrhoea and long-term health complications.
1. Giardiasis
Giardiasis, caused by the Giardia lamblia parasite, is one of the most common waterborne infections in flood-affected areas. This microscopic parasite attaches to the walls of the intestines, leading to prolonged digestive issues that can last for weeks.
How it spreads:
- Drinking or swallowing contaminated floodwater.
- Consuming food that has come into contact with floodwaters.
- Person-to-person transmission in crowded shelters or unhygienic conditions.
Symptoms to watch for:
- Persistent diarrhoea (lasting more than a week)
- Bloating, gas, and stomach cramps
- Fatigue and weight loss due to malabsorption
- Greasy, foul-smelling stools that float
Giardiasis can cause severe dehydration and malnutrition, particularly in children and individuals with weakened immune systems.
2. Cryptosporidiosis
Cryptosporidiosis, caused by Cryptosporidium parasites, is a highly resilient infection that spreads rapidly after floods. This parasite is particularly hard to kill, as it is resistant to standard chlorine treatments in drinking water.
How it spreads:
- Drinking untreated, contaminated water.
- Swimming or wading in floodwater or stagnant water.
- Poor sanitation in crowded flood shelters or relief centres.
Symptoms to watch for:
- Watery diarrhoea that lasts for weeks
- Severe nausea and vomiting
- Stomach cramps and dehydration
- Fever and loss of appetite
Cryptosporidiosis is particularly dangerous for young children, the elderly, and immunocompromised individuals, as it can lead to long-term digestive issues and severe dehydration.
💡 Prevention tip: Boiling water is the most effective way to kill Cryptosporidium, as the parasite can survive in chlorinated water supplies.
3. Amoebiasis
Amoebiasis, caused by the Entamoeba histolytica parasite, is a serious intestinal infection that can cause life-threatening complications if left untreated. The parasite invades the intestinal lining, leading to painful ulcers and internal bleeding.
How it spreads:
- Drinking or eating contaminated food or water.
- Poor hygiene and lack of proper sanitation.
- Direct person-to-person transmission in crowded conditions.
Symptoms to watch for:
- Severe, bloody diarrhoea (often mistaken for dysentery).
- High fever and intense stomach pain.
- Unintentional weight loss and fatigue.
- Liver abscesses in severe cases, leading to upper abdominal pain and fever.
Amoebiasis can cause severe complications, including intestinal perforation or liver infections if not treated promptly.
Fungal and other infections
While bacterial, viral, and parasitic infections often take centre stage in flood-related health concerns, fungal infections and other waterborne diseases pose a significant risk, especially in damp, contaminated environments.
Fungi thrive in warm, humid conditions, making flooded homes and workplaces the perfect breeding ground for fungal spores. Inhaling these spores or coming into direct contact with contaminated water or mud can lead to infections that affect the skin, eyes, respiratory system, and wounds.
1. Skin and eye infections
Floodwaters often carry bacteria and fungi, making skin and eye infections common for those who wade through contaminated water. Cuts, scratches, or insect bites that come into contact with floodwater can quickly become infected, leading to painful skin conditions or even severe wound infections.
How it spreads:
- Direct contact with contaminated floodwater.
- Walking barefoot or with open wounds exposed to flood debris.
- Poor hygiene and damp conditions after flooding.
Symptoms to watch for:
- Skin rashes, redness, and itching.
- Painful sores or blisters that worsen over time.
- Swelling and pus around wounds.
- Eye irritation, redness, or discharge if floodwater enters the eyes.
If left untreated, skin infections can spread deeper into the body, leading to cellulitis or even life-threatening sepsis.
2. Legionnaires' Disease
Legionnaires' disease is a severe lung infection caused by the Legionella bacteria, which thrives in stagnant water and contaminated cooling systems after floods. Inhaling tiny water droplets containing the bacteria can lead to a serious respiratory infection resembling pneumonia.
How it spreads:
- Breathing in aerosolised water droplets from flood-damaged air conditioning, plumbing, or stagnant water.
- Exposure to contaminated showers, taps, or humidifiers after flooding.
- Handling damp, mouldy materials indoors.
Symptoms to watch for:
- High fever and chills
- Severe cough and chest pain
- Shortness of breath and difficulty breathing
- Muscle aches and confusion
Legionnaires' disease can cause life-threatening pneumonia, especially in older adults, smokers, and those with weakened immune systems.
💡 Prevention tip: After a flood, flush plumbing systems before using taps or showers, and clean air-conditioning units thoroughly to remove bacteria.
3. Mould-related illnesses
Mould can spread rapidly across damp walls, ceilings, carpets, and furniture. Mould spores become airborne, leading to respiratory issues, allergies, and worsening of pre-existing conditions like asthma.
How it spreads:
- Inhalation of airborne mould spores in damp, enclosed spaces.
- Prolonged exposure to water-damaged buildings and materials.
- Touching contaminated surfaces covered in mould growth.
Symptoms to watch for:
- Persistent coughing, sneezing, and wheezing
- Watery eyes, runny nose, and skin irritation
- Shortness of breath, especially in those with asthma
- Headaches and sinus congestion
Long-term mould exposure can trigger severe allergic reactions, exacerbate respiratory illnesses, and cause lung infections in immunocompromised individuals.
💡 Prevention tip: Use ventilation, dehumidifiers, and mould-killing treatments like SAN-AIR to prevent fungal growth in flood-affected areas. Remove and discard heavily mould-infested materials.
Conclusion
Floods leave more than just property damage in their wake—they create serious health risks, particularly from waterborne diseases. Contaminated water, damp environments, and poor sanitation allow bacteria, viruses, parasites, and fungi to thrive, increasing the risk of infections that can spread rapidly through affected communities.
Here are key prevention tips to follow during and after a flood:
✅ Avoid drinking or using floodwater unless it has been properly treated. Boil water for at least one minute or use water purification tablets before consuming.
✅ Wash hands regularly with soap and clean water, especially before eating or handling food.
✅ Do not wade, swim, or bathe in floodwater, as it can contain sewage, harmful bacteria, and chemical pollutants. If exposure is unavoidable, wear protective gear such as waterproof boots and gloves.
✅ Dispose of contaminated food immediately—if food has been in contact with floodwater or has an unusual smell or texture, throw it out. Do not consume canned goods if they are dented or damaged.
✅ Disinfect all surfaces in flood-affected homes, especially kitchen counters, utensils, and food storage areas.
✅ Dry out water-damaged spaces quickly to prevent mould growth. Open windows for ventilation, use dehumidifiers, and remove heavily damaged carpets, furniture, or insulation.
✅ Seek medical attention if symptoms of infection appear—such as persistent diarrhoea, vomiting, fever, skin infections, or breathing difficulties. Early treatment can prevent complications.
✅ Ensure vaccinations are up to date, particularly for Hepatitis A, Rotavirus, and even Tetanus, which are common concerns in post-flood environments.
Recovering from a flood is challenging, but taking the right precautions against waterborne diseases can help keep your household safe and healthy.
Protect Yourself After a Flood: Essential Supplies to Keep You Safe
SAN-AIR Mould Removal Range
Flooded homes often breed harmful mould, impacting your air quality and health. The SAN-AIR Mould Removal range uses plant-based, non-toxic ingredients to effectively kill mould and bacteria, making it safe for your family and pets while protecting your home after a flood.
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Australian NaturalCare - Probiotic 32 Billion
A healthy gut is vital when dealing with post-flood challenges like exposure to bacteria or stress. Australian NaturalCare Probiotic 32 Billion is a daily probiotic blend designed to support digestive health, immunity, and overall wellbeing, helping you stay strong from the inside out.
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ViroCLEAR Sanitisers & Disinfectants
When cleaning up after a flood, proper hygiene is crucial, but alcohol-based products can be harsh, especially on sensitive skin. ViroCLEAR’s BKC-based range is a gentler, alcohol-free alternative, offering hospital-grade disinfectants and non-irritating hand sanitisers that kill germs effectively while being safe for your whole family.
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True Blue Wipeout Food Grade Sanitiser 5L
After a flood, kitchens and food preparation areas can easily become contaminated, posing health risks. True Blue Wipeout Food Grade Sanitiser is a versatile surface sanitiser suitable for general cleaning, food prep areas, and sanitising cutlery and utensils. It kills germs effectively while being safe around food, making it an essential tool during your flood recovery cleanup.
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