Bacteria, Viruses, & Parasites in Drinking Water 101

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Bacteria, viruses and parasites pose a serious health risk in drinking water. Germs and pathogens are usually killed or removed during water treatment, but contaminated drinking water may contain these impurities.

This glossary shares information about viruses, parasites, and bacteria in water, including how water becomes microbiologically contaminated, the potential health risks of these contaminants, and how to protect your family from drinking water germs.

❔ What are Bacteria, Viruses & Parasites?

πŸ’‘ Bacteria, viruses, and parasites are disease-causing microorganisms found all around us. Water, soil, and most surfaces harbor some degree of microbiological activity. Some types of bacteria, viruses, and parasites are harmless, but others can cause disease.

There are a few key differences between viruses, bacteria, and parasites:

  • Viruses rely on a host cell for replication
  • Bacteria are about 100 times larger than viruses and live and multiply in the environment
  • Parasite cells are similar to human cells and even have a defined nucleus

Some of the most common water-transmitted viruses are:

  • Norovirus
  • Adenovirus
  • Hepatitis A and E viruses
  • Astrovirus
  • Rotavirus

Some of the most common water-transmitted bacteria are:

  • Escherichia coli
  • Campylobacter jejuni
  • Giardia lamblia
  • Salmonella
  • Legionella pneumophila
  • Cryptosporidium.

Some of the most common water-transmitted protozoan parasites are:

  • Entamoeba histolytica
  • Naegleria spp
  • Toxoplasma gondii
  • Isospora belli
  • Balantidium coli
  • Acanthamoeba spp
  • Sarcocystis spp
  • Cyclospora cayetanensis.
In Water AsBacteria: Escherichia coli, campylobacter jejuni, giardia lamblia, salmonella, legionella pneumophila, cryptosporidium

Parasite: entamoeba histolytica, naegleria spp, toxoplasma gondii, isospora belli, balantidium coli, acanthamoeba spp, sarcocystis spp, cyclospora cayetanensis

Viruses: norovirus, adenovirus, hepatitis A and E viruses, astrovirus, rotavirus
SourcesSewage or leaking septic
Decaying animal waste
Improperly stored or undercooked food
Maximum Contaminant Levels (MCLs)EPA: 0 mg/L
Potential Health RisksGastrointestinal and flu-like symptoms
High risk for people with compromised immune system
Chemical Treatment

🩺 What are the Potential Health Effects of Bacteria, Viruses & Parasites?

Not all microorganisms are dangerous to human health (some bacteria are even good for you). However, to stay on the safe side, you should assume to all pathogens are dangerous. It’s not worth the risk of drinking contaminated water.

Some of the potential health effects of drinking water containing viruses, bacteria, and parasites are:

  • Diarrhea
  • Vomiting
  • Abdominal pain
  • Headaches
  • Nausea
  • Fever
  • Dehydration
  • Fatigue

Different types of pathogens have different health effects (i.e., you may get giardiasis if you swallow giardia germs, which has its own specific symptoms), but most of them impact the intestinal tract. The incubation period for different pathogens varies, too. For instance, giardiasis has a two-week incubation period, while hepatitis A may not appear until 28 days after exposure to the microorganism.

Some pathogens, like E.Coli, can often be fought by your immune system without many more symptoms than stomach cramps. But in worst cases, depending on the pathogens in your water, drinking contaminated water may even lead to death. Some people are more at risk than others, too – healthy people can usually fight off an intestinal infection in a matter of days, but old people, babies, small children, and people with a compromised immune system are more at risk of serious symptoms.

bacteria in water

🚰 How Do Bacteria, Viruses & Parasites Get Into Drinking Water?

Many bacteria, viruses and parasites don’t need person-to-person contact to spread throughout the human population. These microbiological contaminants get into drinking water in the following ways:

  • Through sewage or leaking septic waste – human waste and animal feces can contaminate water systems and treatment plants in areas with leaking or overflowing septic systems or runoff from animal farms. This fecal matter may contain bacteria, viruses, or parasites that can affect the human body.
  • Through dead or decaying animal waste – Water quality may also be affected by animal waste compromising the water supply.

You’re at a higher risk of drinking pathogens if you get your water from private well. Well water systems aren’t regulated by the Environmental Protection Agency (EPA), and contain untreated water. Your well’s location and structural design can affect your likelihood of having your drinking water contaminated by microbes. It’s recommended to test your water at least once a year for coliform bacteria, which often indicates the presence of other pathogens with public health problems.

Microbiological contamination is less common in industrialized countries with good infrastructure. But many states still have to issue the occasional boil water notice if a pathogen is detected in their water. Occasionally, a pathogen may go undetected in a public water supply, leading to widespread contamination.

Keep in mind that coliform bacteria and other pathogens are most likely to be found in recreational water (such as rivers and lakes). You should never drink straight from an untreated water source due to the risk of contamination.

Damaged septic tank

πŸ“‰ Do Water Treatment Facilities Monitor Levels of Bacteria, Viruses & Parasites in Drinking Water?

Yes, water treatment facilities monitor bacteria, viruses, and parasites, and treat water to reduce the risk factors associated with these pathogens.

If your public drinking water tastes a bit like swimming pools, that’s because it has been disinfected with chlorine or chloramine, two chemicals that are used to kill the common pathogens and parasites found in natural water sources.

πŸ“Œ The EPA has Surface Water Treatment Rules that public water systems are obliged to follow to control microbiological contamination. For instance, the EPA requires water systems to remove 99.9% of cryptosporidium, viruses, and giardia parasites. For most pathogens, the EPA has a public health goal of 0, meaning that no contaminants should be present in public drinking water.

To keep public tap water safe, water suppliers test for coliform bacteria and other living cells every day. If any organism is detected, the supplier should issue a boil water notice, asking the public to drink bottled water or bring their tap water to a rolling boil for at least one minute (according to the advice by the Centers for Disease Control and Prevention, or CDC). Customers should continue to follow the boil water notice until further tests indicate that their water is no longer contaminated.

πŸ”Ž How Can I Tell if Bacteria, Viruses & Parasites are in My Drinking Water?

If you have contaminated water, you probably won’t be able to tell by sight, smell, or taste alone. Most microbes are tasteless and odorless, and don’t change the appearance of your water.

So, how can you detect bacteria, viruses, and parasitic infections in your water? Most people only find out that their water is contaminated when infection occurs. Depending on the source of contamination, you may notice the following changes to your water quality:

  • An unusual tinge or color
  • Cloudiness
  • Manure or sulfur odor
  • Suspended solids (which indicate a structural fault in your well, for instance)
Bacteria in water

If you want to know for sure whether you have safe drinking water, without guessing or waiting for common symptoms such as abdominal cramps, we recommend testing your water.

Choose a laboratory you can trust to test for coliform bacteria (which usually indicates the presence of disease-causing pathogens) and other microbes that you’re concerned about. The best laboratories offer a variety of testing packages, including specific tests (e.g. for legionella), broad tests (e.g. total microbiology tests), and tests combining two common pathogens (e.g. for coliform bacteria and E.Coli).

You should receive your test results in one week. In the meantime, if you suspect microbiological contamination, boil your tap water or buy bottled water to avoid getting sick.

πŸ‘©πŸ½β€βš•οΈHow Can I Protect My Family from Bacteria, Viruses & Parasites in Drinking Water?

There are several ways to protect your family from bacteria, viruses, and parasites in drinking water. These include:

  • Install a water filter in your home. If you don’t want to rely on a public supplier to clean your water, or you own a private well, the best way to ensure safe, clean water is to filter it yourself. UV purifiers are popular and safe methods of killing bacteria, viruses, cysts, and other parasites in water. You can also buy a chemical injection system that injects chlorine into water to disinfect it.
  • Take precautions. If your state issues a boil water notice, or you think your well has been contaminated, switch to bottled water or boil your water for at least one minute if you plan to use it for drinking, washing, or preparing food.
  • Disinfect your well. If you own a well, you should test your water for coliform bacteria and shock the water with chlorine every 3 to 5 years. You should also shock your well if you perform well repairs or maintenance, or your water taste or quality changes.
Uv purification system

⚠️ How Else Can I Be Exposed to Bacteria, Viruses & Parasites?

Aside from in your own drinking water, the most common causes of exposure to bacteria, viruses, and parasites are:

  • Through direct contact with, or close proximity to, somebody who is sick with an infectious (spreadable) pathogen. The pathogen may spread through mucus membranes, which line the throat, eyes, nose, and digestive tract, and parts of the body that are exposed to air, like open wounds.
  • By touching infected surfaces, then touching your mouth, nose, or eyes, enabling the pathogen to enter your body.
  • By swimming in lakes or rivers containing traces of fecal matter, parasitic infections, and other microorganisms.
  • By eating contaminated food, such as raw fruits and some undercooked meats.
  • By being in close contact with an infected pet. This is especially likely for parasites like roundworms and hookworms.
  • By drinking water supplies in parts of the world with unsafe drinking water or poor sanitation, such as developing countries.

In most cases, you can limit your exposure to pathogens by following good personal hygiene practices and washing your hands regularly for at least 20 seconds, especially after using the toilet or changing diapers. If any symptoms occur that suggest you may be infected by a microscopic parasite, avoid close contact with other people while you determine the cause of the infection.

πŸ“ Where Can I Get More Information?

Find more information about viruses, bacteria, and parasites in private and public water systems on the sites listed below.

  • Laura Shallcross
    Senior Editor

    Laura is a passionate residential water treatment journalist who holds an undergraduate degree in Print Journalism and a master’s degree in Creative Writing. Over a span of 5 years she's written on a range of topics including water softening, well water treatment, and purification processes.

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