As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
Collected rainwater can carry germs that cause stomach and intestinal illness, especially if the water has washed over a roof, gutters, bird droppings, animal waste, or dirty storage surfaces. Possible infections include giardiasis, cryptosporidiosis, campylobacteriosis, salmonellosis, shigellosis, E. coli infection, hepatitis A, and illnesses caused by viruses such as norovirus.
This does not mean every rain barrel or rainwater tank contains these germs. The risk depends on where and how the water is collected, stored, treated, and used. Rainwater that looks clear can still contain harmful germs or chemicals. The CDC recommends regular testing if collected rainwater will be used for drinking, cooking, or bathing.
Why Rainwater Can Carry Disease
Rain falling through the air is only one part of a rainwater system. The water can pick up contamination before it reaches your tank.
A typical roof collection system follows this path:
Rain → roof → gutter → downspout → tank → pipes or faucet
Each part can add contamination.
Birds, squirrels, rodents, and other animals may leave droppings on the roof. Leaves and dirt can collect in gutters. Insects can enter an uncovered tank. Sediment can build up in the bottom of a cistern.
When rain washes these materials into storage, bacteria, viruses, and parasites may enter with them. The CDC specifically notes that bird droppings and other dirt on roofs can wash into collected rainwater. Contamination can be especially noticeable when rain follows a long dry period.
Diseases Linked to Contaminated Water
Many of the main risks involve germs normally associated with fecal contamination.
| Germ | Illness it can cause | Common symptoms |
|---|---|---|
| Giardia | Giardiasis | Diarrhea, cramps, gas, nausea |
| Cryptosporidium | Cryptosporidiosis | Watery diarrhea, cramps, nausea |
| Campylobacter | Campylobacteriosis | Diarrhea, fever, stomach pain |
| Salmonella | Salmonellosis | Diarrhea, fever, stomach cramps |
| Shigella | Shigellosis | Diarrhea, fever, stomach pain |
| Harmful E. coli | E. coli infection | Diarrhea and stomach cramps |
| Hepatitis A virus | Hepatitis A | Fatigue, nausea, abdominal pain, jaundice |
| Norovirus | Norovirus illness | Vomiting, diarrhea, nausea, stomach pain |
These organisms are among the germs that public-health agencies recognize as possible drinking-water contaminants.
The exact illness cannot be predicted simply by looking at a rain barrel. Different germs require different tests, and many contaminated water samples still look and smell normal.
Stomach Illness Is the Main Concern
Swallowing contaminated water is one of the most important exposure routes.
This can happen when rainwater is used for:
- Drinking
- Making ice
- Cooking
- Brushing teeth
- Washing food that will be eaten
- Filling containers that contact food
Many waterborne infections cause diarrhea, stomach cramps, nausea, vomiting, or fever.
Young children, older adults, pregnant people, and people with weakened immune systems can be more vulnerable to illness from unsafe drinking water.
Rain Barrel Water Is Not Automatically Drinking Water
A basic rain barrel is usually designed for non-potable water.
Non-potable means water that is not intended or confirmed safe for drinking.
A barrel connected directly to a roof downspout may collect:
- Bird and animal droppings
- Pollen
- Dust
- Leaves
- Insects
- Roofing particles
- Bacteria and other microorganisms
Chemicals can also enter rainwater. The CDC notes that contaminants such as lead, copper, and asbestos can come from roofing, gutters, pipes, storage materials, or other surfaces.
These chemical risks are different from infectious diseases, but they are another reason that clear-looking rainwater should not automatically be treated as drinking water.
Does a First-Flush Diverter Make Rainwater Safe?
No.
A first-flush diverter sends the first part of a storm away from the storage tank. That first runoff often carries a large amount of dust, droppings, leaves, and other contamination from the roof.
Using one can improve the quality of collected water. The CDC recommends considering a first-flush device for this reason.
However, a first flush is only a pretreatment step. It does not disinfect water and does not prove that the remaining rainwater is safe to drink.
Germs can still enter later in the storm or grow in the tank and plumbing.
Does a Water Filter Prevent These Diseases?
It depends on the filter and the germ.
A basic sediment filter mainly removes particles. It should not be assumed to remove bacteria, viruses, or parasites.
Even filters designed to remove certain parasites may not remove smaller bacteria or viruses. For example, CDC guidance for Giardia notes that filters designed for cyst removal may still need to be followed by disinfection to address bacteria and viruses.
A drinking-water rainwater system may need several stages, such as:
- Keeping debris and animals out of the collection system.
- Diverting the dirtiest first runoff.
- Removing sediment.
- Using treatment selected for the actual contaminants present.
- Protecting treated water from being contaminated again.
- Testing the finished water.
The correct setup depends on the water source, intended use, local conditions, and test results.
One filter, purifier, UV unit, chemical treatment, or home test should not be treated as proof that roof runoff is potable.
What About UV Treatment?
UV can be useful as one stage of a properly designed water-treatment system because suitable UV equipment can inactivate certain microorganisms.
But UV does not remove dirt, metals, pesticides, roofing chemicals, or other chemical contaminants.
Cloudy or dirty water may also interfere with effective UV treatment, depending on the equipment and operating conditions.
Study common contaminants found in rainwater to understand which maintenance action the latest readings justify.
For drinking-water use, treatment should therefore be designed as a complete system rather than simply adding a UV lamp to a rain barrel.
Can You Get Sick From Bathing in Rainwater?
The risk is usually different from drinking it because you swallow much less water.
However, CDC guidance still recommends testing collected rainwater for germs and chemicals when it will be used for bathing.
Exposure may matter more if water contacts the eyes, nose, open wounds, or is turned into a fine mist. Some waterborne germs can also grow in plumbing and water-using devices rather than coming directly from the original rainfall.
A system supplying showers or other indoor fixtures therefore needs more careful water-quality control than a barrel used only to water ornamental plants.
Mosquitoes Are Another Rain Barrel Health Concern
An open rain barrel can become a mosquito breeding site.
The disease risk is indirect: the stored water provides a place for mosquitoes to reproduce. Whether those mosquitoes can transmit disease depends heavily on the species and location.
Keep tank openings screened and prevent mosquitoes from reaching stored water.
The CDC recommends screening rain barrel openings or regularly emptying simple barrels as part of mosquito control.
A large cistern that cannot be emptied regularly should be designed so insects cannot enter through the inlet, overflow, vents, or other openings.
How to Lower the Risk of Illness
For a typical garden rainwater system, focus first on preventing contamination.
Keep the roof and gutters reasonably clean. Remove leaves and animal debris. Screen tank openings. Keep lids secure. Prevent rodents, insects, and other animals from entering the tank.
A first-flush diverter can reduce the amount of contamination washed into storage during the beginning of a storm.
Also clean the tank and remove accumulated sediment when needed. Inspect pipes, screens, gutters, and fittings for damage.
Most importantly, match water quality to the intended use.
Water used on ornamental plants does not need to meet the same standard as water that someone will swallow.
If You Want to Drink Collected Rainwater
Treat this as a drinking-water system, not as a normal rain barrel project.
The CDC recommends regularly testing rainwater for harmful germs and chemicals when it will be used for drinking, cooking, or bathing. It also recommends contacting the local health department for advice about which contaminants should be tested.
A safer planning process includes:
- Suitable roof and collection materials
- Protection from animal waste and debris
- First-flush diversion or other prefiltration
- Covered, sanitary storage
- Treatment designed for the contaminants that may be present
- Proper maintenance
- Current laboratory testing of finished water
- Protection against contamination after treatment
- Compliance with applicable local drinking-water and plumbing requirements
Do not rely only on taste, smell, clarity, a total dissolved solids meter, or simple home test strips.
A potable system is one intended to provide water suitable for drinking. Making collected roof runoff potable requires more than installing a filter.
When to Seek Medical Advice
If someone becomes ill after drinking untreated or questionable rainwater, tell the healthcare provider about the possible water exposure.
Seek medical care sooner if symptoms are severe, diarrhea is bloody, dehydration develops, symptoms continue, or the person is very young, older, pregnant, or has a weakened immune system.
Testing the person and testing the water are separate issues. A household water test cannot diagnose the cause of someone's illness.
Frequently Asked Questions
Can drinking rainwater give you diarrhea?
Yes. Collected rainwater contaminated with bacteria, viruses, or parasites can cause diarrheal illness. Possible causes include Giardia, Cryptosporidium, Campylobacter, Salmonella, Shigella, harmful E. coli, and norovirus.
Is fresh rainwater safe to drink straight from a rain barrel?
It should not be assumed to be safe. Water entering a rain barrel may have washed across roofing, gutters, animal droppings, dust, and other contaminated surfaces. Clear water can still contain harmful germs.
Can bird poop in a rainwater tank make you sick?
Yes. Bird droppings can carry microorganisms, and rain can wash the droppings from a roof into a barrel or cistern. Keeping roofs reasonably clean and using measures such as first-flush diversion can reduce contamination but cannot guarantee drinking-water safety.
Can Giardia be found in collected rainwater?
Giardia is a waterborne parasite associated with fecal contamination and is one of the pathogens of concern in untreated private water sources. Drinking water contaminated with Giardia can cause giardiasis.
Does boiling rainwater make it completely safe?
Boiling can kill many disease-causing microorganisms, but it does not remove all chemical contaminants. Water contaminated by roofing materials, metals, fuels, or other chemicals may require different treatment and testing. Boiling alone should not be treated as a complete rainwater treatment system.
Can I use rain barrel water on my garden?
Rainwater is commonly used for irrigation, but how it is applied matters. Avoid assuming untreated roof runoff is suitable for uses where people may swallow the water. CDC guidance recommends using a safer water source when possible for washing produce or watering plants that will be eaten.
How can I tell whether my rainwater is safe to drink?
Appearance, smell, and taste cannot confirm safety. Drinking-water use requires suitable collection and treatment plus current laboratory testing for relevant germs and chemicals. Your local health department can advise which tests are appropriate for your area and system.
