Waterborne Diseases: What They Are and How to Prevent Them

Waterborne Disease in the US: About 7.15 Million Illnesses a Year

Most people assume waterborne disease is a developing-world problem. It is not. The CDC estimates that about 7.15 million waterborne illnesses happen in the United States every year, across all the ways we come into contact with water: swimming and recreation, everyday household exposure, and drinking. Drinking water alone accounts for roughly 1.13 million of those illnesses, and it drives a disproportionate share of the serious cases: about 40 percent of the hospitalizations and half of the deaths linked to waterborne pathogens. Some of these pathogens, like Cryptosporidium and Giardia, can survive standard chlorine treatment. Worth knowing up front: most of the hospitalizations and deaths trace to a few opportunistic bacteria that grow inside plumbing and premise water systems, Legionella chief among them, rather than to the stomach-bug pathogens most people picture.

This guide breaks down the most common waterborne diseases found in US water supplies, who is most at risk, and the specific filtration technologies proven to stop each one.

Key Takeaways

What Are Waterborne Diseases?

Waterborne diseases are illnesses caused by microscopic organisms, namely bacteria, viruses, and parasites, that contaminate drinking water. When you swallow, bathe in, or breathe in mist from contaminated water, these pathogens (disease-causing microorganisms) can make you sick.

Understanding the three types of waterborne pathogen matters, because each type calls for a different removal method:

• Bacteria (like E. coli and Salmonella): single-celled organisms removed by UV light, ceramic filters, reverse osmosis, and ultrafiltration.
• Viruses (like norovirus and Hepatitis A): much smaller than bacteria, removed by UV light and reverse osmosis. Ceramic filters alone typically cannot catch them.
• Parasites and protozoa (like Giardia and Cryptosporidium): larger than bacteria but often resistant to chlorine. Removed by ceramic filters, UV light, reverse osmosis, and ultrafiltration.

Common Waterborne Diseases in the United States

Not all waterborne pathogens are equally common or equally dangerous. Here are the seven you should know about, based on CDC waterborne disease surveillance and burden data.

Giardia (Giardiasis)

Giardia is the most common waterborne parasite in the United States. It causes giardiasis, an intestinal infection with symptoms including watery diarrhea, stomach cramps, nausea, and dehydration. Symptoms typically last 2 to 6 weeks.

Giardia cysts resist standard chlorine disinfection, which means they can survive municipal water treatment. They are commonly found in surface water sources contaminated by animal or human waste.

Cryptosporidium (Cryptosporidiosis)

Cryptosporidium is another chlorine-resistant parasite, responsible for some of the largest waterborne disease outbreaks in US history. Symptoms include watery diarrhea, fever, and stomach cramps lasting 1 to 2 weeks.

For healthy adults, cryptosporidiosis is unpleasant but usually resolves on its own. For immunocompromised individuals, such as those undergoing chemotherapy or living with HIV, it can be life-threatening. There is no reliably effective treatment once an immunocompromised person is infected, which makes prevention through water treatment especially important for them.

Legionella (Legionnaires' Disease)

Legionella bacteria cause Legionnaires' disease, a severe form of pneumonia that can be fatal. Unlike most waterborne illnesses, Legionella spreads when you breathe in contaminated water droplets from showers, hot tubs, cooling towers, and decorative fountains. You do not typically catch it from drinking water.

Legionella thrives in warm, stagnant water between 77°F and 113°F. Homes with old plumbing, infrequently used fixtures, or warm water storage tanks carry a higher risk.

E. coli

Most strains of E. coli are harmless, but some, particularly E. coli O157:H7, can cause severe illness including bloody diarrhea, vomiting, and in rare cases kidney failure (a condition called hemolytic uremic syndrome, or HUS). Symptoms typically last 5 to 10 days.

E. coli contamination in water usually comes from agricultural runoff, septic system failures, or sewage overflows reaching well water or municipal supplies.

Norovirus

Norovirus is one of the most common causes of waterborne disease outbreaks in the United States. It is extremely contagious, and even a tiny amount of the virus can make you sick. Symptoms include sudden vomiting, diarrhea, and stomach pain, usually lasting 1 to 3 days.

Because norovirus is a virus, and much smaller than bacteria, ceramic filters alone cannot remove it. UV sterilization or reverse osmosis is needed for virus removal.

Salmonella

Salmonella bacteria cause salmonellosis, with symptoms including diarrhea, fever, and abdominal cramps lasting 4 to 7 days. While most people associate Salmonella with contaminated food, it also spreads through untreated or poorly treated water, especially well water contaminated by animal waste.

Hepatitis A

Hepatitis A is a viral infection that affects the liver, transmitted through water contaminated with fecal matter. Symptoms include fatigue, nausea, stomach pain, and jaundice (yellowing of the skin), and can last several weeks to months. A vaccine is available, but water treatment provides an additional layer of protection.

Waterborne Disease Quick Reference

How Do Waterborne Pathogens Get Into Your Water?

Even in the United States, your water can pick up contamination at several points between the source and your faucet. Understanding how pathogens enter your supply helps you choose the right protection.

Municipal water systems treat water at the plant, but problems can occur after treatment. Aging pipes, some more than 100 years old, can develop cracks that let contaminants in. Water main breaks, pressure drops, and treatment plant malfunctions can all let pathogens through. And chlorine-resistant organisms like Cryptosporidium and Giardia can survive standard treatment. For a broader look at what might be in your tap water, see our guide to common tap water contaminants.

Well water has no municipal treatment at all, so your water comes straight from the ground to your glass. Agricultural runoff, nearby septic systems, and surface water intrusion after heavy rain can introduce bacteria, parasites, and viruses directly into your supply. The EPA notes that private well owners are responsible for their own water testing and treatment.

Your home's plumbing can harbor pathogens too. Biofilm, a slimy layer of bacteria, builds up inside pipes, especially in sections holding stagnant water. Guest bathrooms, vacation homes, and infrequently used fixtures are particularly vulnerable to Legionella growth in warm water lines.

Natural disasters like floods, hurricanes, and wildfires can overwhelm treatment plants and contaminate well water, leading to boil water advisories that affect millions of Americans each year.

Who's Most at Risk for Waterborne Illness?

Anyone can get sick from contaminated water, but certain groups face much higher risks of severe illness. Learn more about protecting your household in our guide to water safety for families.

• Infants and young children, whose immune systems are still developing.
• Adults over 65, as immune response weakens with age.
• Pregnant women, since infection risks extend to the developing baby.
• Immunocompromised individuals, including those undergoing chemotherapy, organ transplant recipients, and people living with HIV.
• Private well owners, because without municipal treatment, well water is only as safe as the treatment you add.
• Residents in older neighborhoods, where aging infrastructure means greater risk of contamination in the distribution system.

For these groups, point-of-use water treatment is not optional. It is essential.

How to Protect Your Family from Waterborne Diseases

Waterborne diseases are preventable. With the right testing and treatment, you can sharply reduce your family's exposure to waterborne pathogens. Here is the three-step approach.

1. Test your water first

   You cannot treat what you do not know about. Test for bacteria and coliform at least once a year, and immediately after any flooding, a change in taste or smell, or nearby construction. Municipal water users should request their utility's Consumer Confidence Report (CCR).

2. Choose the right filtration technology

   Different pathogens call for different removal methods. UV sterilization destroys viruses, bacteria, and parasites. Ceramic filtration physically blocks bacteria and cysts. Reverse osmosis removes pathogens plus chemical contaminants. Match your system to the specific threats in your water.

3. Use boiling as a backup

   When filtration is not available, boil water at a rolling boil for at least 1 minute (3 minutes above 6,500 feet). This kills bacteria, viruses, and parasites, though it does not remove chemical contaminants.

Step 1: Test Your Water

If you are on well water, our complete guide on how to test your well water walks you through the process. Municipal water users can follow our guide on how to test your water at home.

Not sure where to start? A home bacteria test kit gives you a baseline reading of your water's microbiological safety, with no lab appointment needed.

Step 2: Choose the Right Filtration Technology

Here are the four proven technologies for waterborne pathogen removal.

UV Sterilization uses germicidal ultraviolet light at a 254nm wavelength to disrupt the DNA of bacteria, viruses, and protozoa, achieving up to 99.99 percent reduction without adding any chemicals to your water. The recognized performance benchmark for UV disinfection is NSF/ANSI Standard 55, which is the standard to look for when you compare UV systems. UV does need pre-filtration, because particles can shield organisms from the light if the water is cloudy or high in sediment. For a deeper look at the technology, see our guide to how UV water purification works.

Crystal Quest UV Sterilizer Systems

Destroys bacteria, viruses, and parasites with up to 99.99 percent effectiveness using germicidal UV light, with no chemicals added. Available from point-of-use units to whole-home flow rates.

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Ceramic Filtration works as a mechanical barrier. Water passes through microscopic pores as small as 0.5 microns (a human hair is about 70 microns wide). This physically blocks bacteria like E. coli and Salmonella, and cysts like Cryptosporidium and Giardia. One important caveat: ceramic filters cannot reliably remove viruses. If viruses are a concern, pair ceramic filtration with UV, or choose an RO system. Crystal Quest's ceramic under-sink filter systems and ceramic countertop systems use cleanable cartridges you can reuse across a long service life.

Reverse Osmosis (RO) pushes water through a membrane with pores so tiny that essentially only water molecules pass through. RO removes bacteria, viruses, cysts, and dissolved chemical contaminants like lead, arsenic, and PFAS, typically rejecting 95 percent or more of most contaminants. It is the most comprehensive single treatment technology available. See our guide on how reverse osmosis works for a deeper explanation.

Ultrafiltration (UF) uses membranes with 0.02-micron pores, small enough to block bacteria, parasites, and most viruses while allowing beneficial minerals to pass through. Learn more about how ultrafiltration works and where it fits relative to ceramic and RO.

For the broadest protection, consider a multi-barrier approach: sediment pre-filtration catches large particles, carbon filtration removes chemicals and improves taste, and a final UV or RO stage eliminates pathogens. Think of it as an assembly line where each stage handles one specialized job.

Which Technology Removes Which Pathogens?

Step 3: Boiling and Boil Water Advisories

Boiling is a reliable backup method. Bring water to a rolling boil for at least 1 minute (3 minutes above 6,500 feet in elevation). This kills bacteria, viruses, and parasites effectively.

When a municipal boil water advisory is issued, our boil water advisory guide walks through exactly what to do. In short:

• Boil all water used for drinking, cooking, brushing teeth, and making ice.
• Use bottled water for infant formula and any medical needs.
• Flush your ice maker. Discard existing ice and run several fresh cycles after the advisory lifts.
• Avoid swallowing water in the shower.
• Disinfect your plumbing after the advisory lifts by flushing all faucets for several minutes.

Homeowners with UV sterilizers or reverse osmosis systems already in place have continuous protection, even when municipal advisories are issued. These systems treat water at the point of use, providing an independent layer of safety regardless of what is happening at the treatment plant.

Frequently Asked Questions

What are the most common symptoms of waterborne illness?

The most common symptoms are diarrhea, nausea, vomiting, stomach cramps, and fever. Some waterborne diseases cause more severe symptoms: Legionella can cause pneumonia, E. coli O157:H7 can lead to kidney failure, and Hepatitis A affects the liver. If you have persistent symptoms after possible exposure to contaminated water, see a doctor.

Can tap water make you sick from bacteria?

Yes. Even treated municipal tap water can contain chlorine-resistant parasites like Cryptosporidium and Giardia. Aging pipes, water main breaks, and treatment plant malfunctions can also introduce bacteria into treated water. Well water faces even higher risk, since it receives no municipal treatment at all.

Does boiling water remove all bacteria and viruses?

Boiling water at a rolling boil for at least 1 minute (3 minutes above 6,500 feet) effectively kills bacteria, viruses, and parasites. However, boiling does not remove chemical contaminants, heavy metals, dissolved solids, or sediment. For protection against both biological and chemical threats, a filtration system like reverse osmosis is a more comprehensive option.

What water filter removes bacteria and parasites?

UV sterilizers, ceramic filters (0.5 microns or smaller), and reverse osmosis systems all effectively remove bacteria and parasites. For viruses, you need UV sterilization or reverse osmosis, because ceramic filtration alone cannot catch them due to their smaller size. A multi-stage system that combines pre-filtration with UV or RO provides the broadest protection.

How do you test your water for bacteria at home?

Home bacteria test kits give reliable results from a simple water sample. Well water should be tested at least once a year, plus after any flooding, a change in taste or smell, or nearby construction. For municipal water, request your utility's Consumer Confidence Report and consider independent testing after any advisory.

Are waterborne diseases common in the United States?

Yes, far more common than most people realize. The CDC estimates about 7.15 million waterborne illnesses occur in the US each year across all exposure routes, resulting in roughly 118,000 hospitalizations and 6,630 deaths. Drinking water alone accounts for about 1.13 million of those illnesses. While US water treatment infrastructure is among the best in the world, aging pipes, chlorine-resistant organisms, and untreated well water all contribute to ongoing risk.

Does reverse osmosis remove bacteria?

Yes. Reverse osmosis membranes have pore sizes small enough to reject bacteria, viruses, and cysts, along with dissolved chemical contaminants like lead, arsenic, and PFAS. RO typically rejects 95 percent or more of most contaminants, which makes it one of the most comprehensive single water treatment technologies available.

What is the best water purification method for pathogens?

It depends on which pathogens you need to remove. UV sterilization is a gold standard for microbiological treatment, disrupting bacteria, viruses, and protozoa with up to 99.99 percent effectiveness. Reverse osmosis removes pathogens plus chemical contaminants like lead and PFAS, which makes it the most comprehensive single technology. Ceramic filtration is effective against bacteria and parasitic cysts but cannot remove viruses. For the broadest protection, a multi-barrier approach that combines sediment pre-filtration, carbon treatment, and a UV or RO stage covers all pathogen types and chemical threats.

How long do waterborne illness symptoms last?

Duration varies a lot by pathogen. Norovirus symptoms typically resolve in 1 to 3 days. E. coli infections last 5 to 10 days. Cryptosporidiosis runs 1 to 2 weeks. Giardiasis can persist for 2 to 6 weeks. Hepatitis A symptoms may last weeks to months. Immunocompromised individuals often experience longer and more severe illness from any waterborne pathogen.