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Contaminated water can carry bacteria, viruses, and parasites that cause serious illness. Common water-related diseases include cholera, typhoid fever, hepatitis A, giardiasis, cryptosporidiosis, and several types of diarrheal infection.
The important point is that the water itself does not create these diseases. The problem is the disease-causing germs in the water. Human or animal waste is a common source. Contaminated food, dirty hands, and direct contact can spread many of the same diseases. The World Health Organization (WHO) lists unsafe water and poor sanitation as important routes for diseases such as cholera, dysentery, hepatitis A, typhoid, and polio.
For rainwater users, this matters because roof runoff can pick up bird droppings, animal waste, dirt, and other contamination before entering a barrel, IBC tote, or cistern.
10 Diseases That Can Be Spread Through Contaminated Water
| Disease | Cause | Common signs |
|---|---|---|
| Cholera | Vibrio cholerae bacteria | Severe watery diarrhea, dehydration |
| Typhoid fever | Salmonella Typhi bacteria | Fever, weakness, stomach pain |
| Shigellosis | Shigella bacteria | Diarrhea, cramps, fever |
| Hepatitis A | Hepatitis A virus | Tiredness, nausea, jaundice |
| Giardiasis | Giardia parasite | Diarrhea, gas, stomach cramps |
| Cryptosporidiosis | Cryptosporidium parasite | Watery diarrhea, stomach cramps |
| E. coli infection | Harmful strains of E. coli | Diarrhea, cramps, vomiting |
| Salmonellosis | Salmonella bacteria | Diarrhea, fever, stomach cramps |
| Campylobacteriosis | Campylobacter bacteria | Diarrhea, fever, stomach pain |
| Leptospirosis | Leptospira bacteria | Fever, headache, muscle pain |
These diseases have different transmission routes. Contaminated water is only one possible route for some of them.
1. Cholera
Cholera is a bacterial infection caused by Vibrio cholerae. People can become infected by consuming food or water contaminated with the bacteria.
The main danger is severe watery diarrhea. A person can lose a large amount of water and salts very quickly. Without proper treatment, severe dehydration can become life-threatening. WHO describes cholera as an acute diarrheal infection associated with contaminated food and water.
Cholera is most strongly linked with places where safe drinking water and sanitation systems are limited or disrupted.
2. Typhoid Fever
Typhoid fever is caused by Salmonella Typhi. The bacteria usually spread when food or water becomes contaminated with waste from an infected person.
Possible symptoms include prolonged fever, headache, tiredness, stomach pain, nausea, constipation, or diarrhea. Severe infections can cause serious complications.
WHO states that typhoid is usually spread through contaminated food or water.
3. Shigellosis and Dysentery
Shigellosis is an intestinal infection caused by Shigella bacteria. Some infections cause severe diarrhea containing blood, which may be described as dysentery.
People can become infected by drinking water contaminated with human waste. The bacteria can also spread through food, dirty hands, surfaces, and close contact.
The CDC notes that only a small amount of Shigella is needed to make someone sick.
Common symptoms include diarrhea, fever, stomach pain, and the feeling that you still need to have a bowel movement even when your bowels are empty.
4. Hepatitis A
Hepatitis A is a viral infection that affects the liver.
The virus can spread when someone consumes food or water contaminated with waste from an infected person. Poor sanitation and unsafe drinking water can increase the risk. WHO identifies contaminated food and water as important routes of hepatitis A transmission.
Symptoms can include:
- Tiredness
- Fever
- Loss of appetite
- Nausea
- Stomach pain
- Dark urine
- Pale stools
- Yellow skin or eyes, called jaundice
Not everyone develops noticeable symptoms.
5. Giardiasis
Giardiasis is caused by a microscopic parasite called Giardia.
The parasite leaves an infected person or animal through feces. If that waste reaches water, another person can become infected by swallowing the contaminated water.
Untreated streams, lakes, shallow wells, and other unsafe water sources can contain Giardia.
Common symptoms include diarrhea, gas, nausea, stomach cramps, dehydration, and greasy or foul-smelling stools.
Giardia is also a good example of why treatment systems need more than a random cartridge filter. Different germs have different resistance and removal requirements.
6. Cryptosporidiosis
Cryptosporidiosis is caused by the microscopic parasite Cryptosporidium, often called Crypto.
The planning note “How Sanitary Is Rainwater?” shows why intended use matters when choosing treatment.
The parasite can enter water through feces from infected people or animals. People become infected after swallowing the organism.
Watery diarrhea is the most common symptom. Stomach cramps, nausea, vomiting, fever, dehydration, and weight loss can also occur.
Crypto is especially important when planning water treatment because it can survive some normal disinfection conditions. A treatment method that works against one type of germ does not automatically work against every parasite, bacterium, and virus.
7. E. Coli Infection
Most Escherichia coli, or E. coli, bacteria are harmless. Some strains can cause serious intestinal illness.
Disease-causing E. coli can spread through contaminated food, drinking water, animals, and human or animal waste.
Symptoms depend on the strain but may include:
- Watery or bloody diarrhea
- Severe stomach cramps
- Vomiting
- Mild fever
Some types can cause serious complications, especially in young children, older adults, and other vulnerable people.
Finding E. coli in a water test can also be an important sign of fecal contamination.
8. Salmonellosis
Salmonellosis is caused by Salmonella bacteria.
Food is a common source, but people can also become infected after drinking or having contact with contaminated water. Animals and animal waste can also spread the bacteria.
Common symptoms include diarrhea, stomach cramps, and fever. Some people also develop nausea, vomiting, or headaches.
Stored rainwater can be exposed to animal contamination if birds, rodents, insects, or other animals can reach the roof, gutters, tank openings, or stored water.
9. Campylobacteriosis
Campylobacteriosis is an intestinal illness caused by Campylobacter bacteria.
Raw poultry is a major source, but untreated contaminated water can also cause infection.
Symptoms commonly include diarrhea, fever, and stomach cramps. Nausea and vomiting may also occur.
Consider contamination risks in fresh rainwater to assess routine maintenance needed for dependable operation.
As with other fecal bacteria, keeping animal waste away from a water catchment is an important part of lowering risk.
10. Leptospirosis
Leptospirosis is different from many of the other diseases on this list.
It is caused by Leptospira bacteria found in the urine of infected animals. The bacteria can enter water or wet soil. People may become infected by drinking contaminated water or when contaminated water contacts their eyes, mouth, or damaged skin.
Risk can increase after floods and heavy rainfall because animal urine can wash into standing water and other water sources.
Symptoms can include fever, headache, muscle aches, nausea, vomiting, diarrhea, red eyes, and jaundice. Severe disease can affect the kidneys, liver, lungs, or nervous system.
How Water Becomes Contaminated
Disease-causing germs often enter water through human or animal waste.
Common contamination routes include:
- Sewage leaks or overflows
- Failing septic systems
- Floodwater
- Animal droppings
- Rodent urine
- Agricultural runoff
- Dirty water-storage containers
- Contaminated hands or equipment
- Open or poorly protected tanks
Stormwater can also pick up germs and chemicals as it moves across surfaces.
For a household rainwater system, contamination can occur anywhere along the path from the roof to the tap.
Can Collected Rainwater Carry Disease-Causing Germs?
Yes.
Rain falling through clean air may start with relatively little contamination, but harvested rainwater does not stay isolated from its surroundings.
The explanation of limits in “Is Rainwater 100% Clean?” connects the measurement to a practical water-safety decision.
A roof can collect:
- Bird and rodent droppings
- Insects
- Leaves and plant matter
- Dust
- Dirt
- Airborne particles
- Material from gutters and pipes
Those materials can wash into a rain barrel or cistern during the next storm.
The CDC advises that collected rainwater is not necessarily safe for drinking without appropriate removal of germs and chemicals. Testing is particularly important when harvested rainwater is used for drinking, cooking, or bathing.
A covered tank, clean gutters, screened openings, and a first-flush diverter can help reduce contamination. A first-flush diverter sends away some of the first roof runoff from a storm, when dirt and debris may be most concentrated.
These steps improve the system, but they do not prove that the remaining water is safe to drink.
Does Filtering Rainwater Prevent These Diseases?
Filtering can be part of a water-treatment system, but a single filter should not be treated as proof that rainwater is safe to drink.
Different treatment stages do different jobs.
A coarse screen might catch leaves. A sediment filter might remove small particles. A finer filter may remove certain parasites if it is designed and certified for that purpose. Other treatment methods may be needed for bacteria and viruses.
Chemical contamination creates another issue. Boiling can kill many disease-causing germs, for example, but it does not remove most chemical contaminants.
CDC guidance for Giardia also makes this distinction clear: some filters that remove parasites do not remove bacteria or viruses, so additional treatment may be necessary.
If collected rainwater will be potable, meaning used as drinking water, treat safety as a whole-system issue. Collection materials, prefiltration, treatment, storage, plumbing, current laboratory testing, maintenance, and local requirements all matter.
Ways to Reduce the Risk in a Rainwater System
For non-potable uses such as landscape irrigation, the treatment requirements may be much simpler than they are for drinking water. Still, good system design reduces contamination and maintenance problems.
Useful measures include:
- Keep the roof and gutters reasonably clean.
- Prevent animals from entering storage tanks.
- Screen tank openings and vents.
- Keep lids and access covers secured.
- Remove accumulated sediment when needed.
- Prevent contaminated floodwater from entering the tank.
- Use a properly designed first-flush system when appropriate.
- Keep potable plumbing separate from non-potable rainwater plumbing.
- Maintain filters and treatment equipment on schedule.
- Test water when its intended use requires verification.
CDC lists cisterns and storage tanks among private water sources that can be affected by microbial contamination such as Campylobacter, Cryptosporidium, E. coli, Giardia, hepatitis A, Salmonella, and Shigella.
When Waterborne Illness Needs Medical Attention
Diarrhea and vomiting can cause dehydration, especially in young children, older adults, and people who are already ill.
Seek medical advice if symptoms are severe, persistent, or unusual. Warning signs can include bloody diarrhea, severe dehydration, high fever, jaundice, very little urination, severe weakness, or symptoms after known exposure to contaminated floodwater.
Anyone who suspects leptospirosis after floodwater or animal-urine exposure should contact a healthcare provider promptly.
Do not try to identify a waterborne disease only from symptoms. Many of these infections look similar, and proper testing may be needed.
Frequently Asked Questions
What is the most common illness caused by contaminated water?
Diarrheal disease is one of the biggest health problems linked with unsafe water worldwide. Many different bacteria, viruses, and parasites can cause diarrhea, so diarrhea itself does not identify the specific germ. WHO notes that a large share of diarrheal disease can be prevented through safe drinking water, sanitation, and hygiene.
Can rain barrel water make you sick?
It can if disease-causing germs or harmful chemicals are present and the water is used in a way that creates exposure. Roof runoff can pick up contamination from bird droppings, animals, roofing materials, gutters, and airborne pollution. Rain barrel water should not automatically be treated as drinking water.
Can you tell if contaminated water is unsafe by looking at it?
No. Water can look clear and have no unusual smell while still containing disease-causing germs or harmful chemicals. Appearance alone cannot confirm drinking-water safety.
Does boiling contaminated water make it safe?
Boiling is effective against many disease-causing germs when done according to public-health guidance, but it does not solve every water-quality problem. It does not remove most chemical contaminants. Water from a questionable rainwater source may need a broader treatment and testing plan.
Does a first-flush diverter make rainwater safe to drink?
No. A first-flush diverter can reduce some dirt and contamination washed from a roof at the start of rainfall, but it is only one part of a rainwater system. It does not provide complete treatment or verify that the water is potable.
What diseases can animal waste spread through water?
Animal feces or urine can contribute to several infections, including giardiasis, cryptosporidiosis, some E. coli infections, salmonellosis, campylobacteriosis, and leptospirosis. The exact risk depends on the animal, germ, water source, and type of exposure.
Should rainwater used for drinking be tested?
Yes. If harvested rainwater will be used for drinking, cooking, or another use where people may ingest it, current laboratory testing should be part of the safety plan. Testing should be paired with suitable collection, treatment, maintenance, and applicable local health or plumbing requirements rather than used as a one-time guarantee that the system will remain safe.
