21 Drinking Water Bacteria, Viruses, Parasites, and Toxins

Most people in the United States assume their water is safe. The federal government, after all, requires water suppliers to follow certain rules and uphold standards of sanitation. Unfortunately, drinking water contamination is more common than people believe. Additionally, the Natural Resources Defense Council (NRDC) issued a report in 2015 that stated that 77 million people in the US – or about a quarter of the population – got their water from suppliers that didn’t follow the guidelines.

Consequently, people are more vulnerable to the toxins and microorganisms found in contaminated drinking water than they believe. The following article describes some of the more common microorganisms and toxins that cause drinking water contamination.

Bacteria in Drinking Water

1) Cyanobacteria

Cyanobacteria are bacteria that resemble algae. That, plus their color, have sometimes led to their also being called “blue-green algae.” People get exposed to cyanobacteria largely by ingesting or bathing in contaminated water.

Different species of cyanobacteria produce different toxins that are classified by the effects they have on people. Genera like Anabaena or Microcystis produce hepatotoxins that damage the liver. Some genera can produce neurotoxins, and others produce toxic alkaloids that affect the kidneys or gastrointestinal system.

2) Coliform bacteria

Coliform bacteria are rod-shaped bacteria that don’t form spores, can ferment lactose, and are Gram-negative. They are often found in the digestive tract, and many genera are also found in wastewater along with pathogenic bacteria, parasites, and viruses.

While most coliform bacteria are harmless to humans, there are exceptions including the infamous E. coli, which can cause infections of the digestive tract and urinary tract in adults. It can also cause meningitis in newborn infants.

Other pathogenic coliform bacteria include Klebsiella pneumoniae, which can cause pneumonia and gastrointestinal infections. It can also cause secondary infections, especially in people who are in the hospital. Citrobacter and Enterobacter can also cause a variety of infections.

People can use the Coliert test to determine if a water sample contains coliform bacteria. They add a special powder to a water sample and let it incubate for a day. If the water becomes a darker yellow than that of a control sample, it contains coliform bacteria. A variation of the Coliert test can also be used to detect E.coli in water.

3) Leptospira

Leptospira causes an infection called leptospirosis. The disease is spread by soil or water that has been contaminated by the urine of infected people or animals. The bacteria can infect many mammals including horses, cattle, pigs, rodents, and dogs. Symptoms of leptospirosis in dogs can include stiffness, refusal to eat, extreme weakness, fever, abdominal pain, diarrhea, and severe muscle pain.

A human with leptospirosis may have no symptoms, or they may have symptoms such as jaundice, reddened eyes, rash, abdominal pain, high fever, chills, and aching muscles. Leptospirosis can have two stages, with the second stage being far more severe. Second-stage leptospirosis can be associated with meningitis, liver failure, or kidney failure. Untreated leptospirosis can kill.

4) Campylobacter

Campylobacter is considered the most common cause of bacterial gastroenteritis in the world. While the bacteria are primarily transmitted by contaminated food, they can also be transmitted by contaminated water. The can infect many animals including cats, dogs, sheep, pigs, cattle, ostriches, chickens, and even some shellfish.

Symptoms of campylobacteriosis can include the following: bloody diarrhea, nausea, vomiting, abdominal pain, headache, and fever. Most patients develop symptoms two to five days after infection, and the symptoms generally last for three to six days. While most patients recover, the disease can be fatal to the very young, the very old, and people with weakened immune systems.

5) Salmonella

Salmonella is a bacteria genus belonging to the family Enterobacteriaceae. While there are only two species, those two species are subdivided into multiple subspecies and thousands of serotypes (variations). S. enterica affects warm-blooded animals, while S. bangori affects cold-blooded animals, especially reptiles.

Salmonella usually stays within the digestive tract and causes an infection called salmonellosis that causes symptoms like diarrhea and vomiting. If the bacteria spread into a patient’s bloodstream, they can cause typhoid fever or paratyphoid fever. People can contract these diseases by ingesting water contaminated by the feces of an infected person.

6) Vibrio cholerae

Vibrio cholerae is one of the bacteria in drinking water, and it is the bacterium that causes cholera. While some people don’t develop symptoms, others develop symptoms within two or three days of infection. Symptoms include vomiting, diarrhea, and leg cramps. While most people experience only mild symptoms, about ten percent develop symptoms that are severe enough to be life-threatening. While cholera is rare in the US, it is far more common in countries with poor sanitation. Cholera is epidemic in parts of Africa, Asia, and Latin America

Viruses in Drinking Water

7) Enterovirus

The word “enterovirus” actually describes an entire family of over 60 viruses. The ones that caused polio have been eradicated in the Americas. Other enteroviruses can cause viral or aseptic meningitis, and the symptoms of that include a stiff neck, fever, nausea, vomiting, and a severe headache. Other enteroviruses can cause symptoms resembling those of the flu or a cold.

People contract enteroviruses by ingesting water contaminated by feces from an infected person. In some cases, contaminated water will find its way into water sources such as wells.

8) Enteric adenovirus

Members of the Adenovirus genus are better known for causing respiratory illnesses, but the enteric adenovirus causes viral gastroenteritis, which is transmitted by ingesting contaminated water or food. Viral gastroenteritis causes nausea, vomiting, headache, stomach ache, fever, and diarrhea. The symptoms generally last between two and nine days. Most patients are children; in fact, enteric adenovirus is believed to cause between five and twenty percent of the gastroenteritis cases in children.

9) Hepatitis A Virus

The hepatitis A virus (HAV) is one of the viruses in drinking water. It can also be spread by close physical contact with an infected person. Most people develop symptoms within two to four weeks after contracting the virus. Those symptoms range from mild to severe, and can include fever, jaundice, loss of appetite, unusually dark urine, abdominal pain, diarrhea, and vomiting. Symptoms are more severe in adults than in children; children may not have any symptoms at all. Hepatitis A is most common in areas with poor sanitation. People travelling to such regions should get vaccinated beforehand.

10) Norovirus

Norovirus is a highly infectious virus that is the chief cause of foodborne disease in the United States. It can also be transmitted by ingesting contaminated water and contact with an infected person. People can also become infected by touching a contaminated surface and then putting their hand in their mouth. Outbreaks of Norovirus are most common from November to April.

Norovirus causes what people call “stomach flu” or “stomach bug.” Most people develop symptoms within a day or two of being infected. Those symptoms are caused by inflammation of the intestines and/or stomach; the medical term for such inflammation is “acute gastroenteritis.” The symptoms last from one to three days and include nausea, vomiting, stomach pain, and diarrhea. The frequent vomiting and diarrhea can cause the patient to become dehydrated, and symptoms of dehydration include a dry mouth and throat, decrease in urination, and dizziness when standing.

11) Rotavirus

Rotavirus was the leading cause of severe diarrhea in US children under five until the introduction of a vaccine in 2006. It is still the world’s most common cause of severe diarrhea in small children. Roughly 215,000 children throughout the world died from Rotavirus in 2015.

Rotavirus is most common in small children, and it can occur in adults, particularly older adults, adults with weakened immune systems, and healthcare workers treating youngsters with rotavirus.

Most patients develop symptoms about two days after being infected. Symptoms typically include fever, abdominal pain, vomiting, and severe watery diarrhea. The diarrhea and the vomiting can last from three to eight days, putting the patient at risk of dehydration. Symptoms are less severe in adults than in children.


Parasites in Drinking Water

12) Cryptosporidium

Cryptosporidium is a genus of parasitic protozoan that can cause a disease called cryptosporidiosis. It caused the 1993 Milwaukee Cryptosporidiosis Outbreak, the largest outbreak of a waterborne disease in the recorded history of the United States. The parasite contaminated a water plant and thus infected 403,000 people – about a quarter of the city’s population.

The symptoms of cryptosporidiosis include watery diarrhea, nausea, cramps, and headaches. Most patients develop symptoms two to twenty-five days after being infected, and those symptoms typically last one or two weeks. Some patients, however, remain ill for about a month.

13) Dracunculus medinensis

Dracunculus medinensis causes Guinea worm disease and is found only in some African countries. People contract the parasite by ingesting water containing “water fleas” or tiny copepods that are hosts to the worm’s larvae that make their way through the body. Female larvae grow into adults over the next 10 to 14 months. At this point, it starts to emerge in order lay its eggs. In most cases, it comes out of a foot or leg. The worm does not cause any symptoms until its emergence, when it causes pain, fever, and swelling. The host can also develop a secondary infection.

14) Entamoeba histolytica

Entamoeba histolytica is a parasitic amoeba that causes amoebic dysentery, a type of bloody diarrhea. While some people show no symptoms or mild stomach aches, others develop full-blown dysentery with severe diarrhea that produces bloody stools, fever, severe stomach pain, and rapid weight loss. Amoebic dysentery causes hundreds of thousands of deaths worldwide per year. It is most common in developing areas with poor sanitation.

15) Giardia

Giardia is one of the parasites in drinking water. It is a protozoan that can be found throughout the United States and other parts of the world. It is the most commonly diagnosed intestinal parasite in the US, and it is also a common cause of chronic diarrhea in travelers.

In addition to diarrhea, symptoms of giardiasis can include flatulence, dehydration, abdominal cramps, nausea, vomiting, and greasy stools with a tendency to float. Giardiasis can last anywhere from two to six weeks, and there are medications that can ease the symptoms and shorten the disease’s duration.

16) Toxoplasma gondii

Toxoplasma gondii may be one of the most successful parasites in the world, for it has infected 40 million people in the United State alone. It can be contracted by ingesting contaminated water or food. Cats are famously one of the main hosts of the parasite, and people can thus contract it by not washing their hands after cleaning the litterbox.

Healthy hosts usually show no symptoms, for their immune system can keep the parasite under control. If the patient does develop symptoms, they tend to resemble those of the flu – but they can last for months before fading.

If a woman contracts toxoplasmosis while pregnant, she will pass the condition onto her child. A newborn with congenital toxoplasmosis may not show any symptoms at first, but they may develop seizures, mental disability, and eye problems later on. Toxoplasmosis can also cause miscarriage or stillbirth

Toxins in Drinking Water

17) Arsenic

Arsenic is one of the toxins in drinking water. It is sometimes used in a variety of industrial processes and thus ends up in water through improper disposal. Arsenic can also occur in the ground naturally, where it can contaminate a well that was placed too close to it.

Acute arsenic poisoning can cause gastrointestinal symptoms like diarrhea and vomiting. Severe cases can kill. Long-term exposure to arsenic can cause several different types of cancer.

18) Copper

Copper is a metal, and human activities like mining, farming, and manufacturing can release it into the environment. Found in waste water, Cooper can contaminate lakes and rivers.

Often combined with other metals to make bronze and brass, and these alloys are made into pipes and faucets. Water, especially if it is somewhat acidic, can thus contain a lot of copper. The best and easiest way to reduce one’s exposure to copper is to let the faucet run for at least 15 seconds before using or drinking the water. Doing so will dramatically lower the amount of copper in the water.

While small amounts of copper are actually beneficial, larger doses are harmful. High doses of water-borne copper can cause gastrointestinal symptoms like diarrhea and nausea. Extremely high doses of copper can damage the kidneys and liver and even kill.

19) Lead

Lead is the chief toxin found in Flint, Michigan’s water. There, corroded pipes are releasing roughly ten times the allowed amount into the water. Lead can damage almost every organ in the body, and children are particularly vulnerable to its effects that include developmental delays, stunted growth, brain damage, and deafness. Lead can also damage the kidneys and cardiovascular system.

While lead is generally believed to be more of a problem in older buildings, new brass faucets and fixtures can also contain lead. There is thus no guarantee that a building constructed less than twenty years ago will be lead-free.

20) Perchlorate

Perchlorate is a common poisonous chemical used to make explosives, road flares and rocket fuel. While it has been found in the water of 26 states, there are so far no standards or regulations concerning its presence in potable water. The NRDC even sued the EPA for its failure to establish any standards. Perchlorate can interfere with the thyroid’s ability to produce hormones.

21) PFAS

Perfluoroalkyl substances or PFAS are a group of synthetic chemicals that can dissolve in water. They were first used commercially in the 1950s and are found in a variety of products like non-stick pans, clothing, and carpets. They take a long time to break down and thus accumulate within the body. Researchers believe that PFAS can cause birth defects, affect the immune system, increase cholesterol levels, and increase the risk of cancer.


The NRDC provides advice on how to protect yourself from water-borne contaminants. For example, they recommend using a filter certified by the NSF that can be attached to the faucet. A whole house water filter may be an excellent choice. There are different types of filters designed to screen out different contaminants.

Bottled water is not always safer than tap water. Look for brands that have been treated through distillation, reverse osmosis, or filtration with a filter of one micron or smaller. Similarly, boiling water does not always make it safer, for it can actually increase the concentration of toxins like PFAS.


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