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Heads up: This compilation isn't for the squeamish. Hidden within your tap water are unseen entities, thriving and multiplying in unimaginable numbers within every sip of cool, refreshing water you consume. While they may sound alarming, most of these microorganisms are harmless. However, once you see them up close, the images might stay with you forever. Here are 10 microorganisms that could be present in your drinking water right now.
10. Cryptosporidium
Municipal water systems treat water through multiple filtration and disinfection stages before distributing it to households. This process is essential because water sourced from lakes and rivers often contains bacteria. While filtration removes the majority of these microorganisms, it’s not foolproof. As a result, many people may ingest trace amounts of cryptosporidium daily without even realizing it.
Cryptosporisium, a protozoan—essentially a single-celled organism—is notorious for causing severe diarrhea, a condition commonly known as cryptosporidiosis. Acting as a parasite, it attaches itself to the intestines and deposits eggs in fecal matter, facilitating its spread. Contaminated drinking water with infected feces allows crypto to infect new hosts. Although safeguards exist to prevent such outbreaks, they are only about 99 percent effective. A notable incident occurred in 1998 in Sydney, Australia, where a crypto outbreak was detected. Authorities delayed action as the contamination levels were deemed “within acceptable health limits,” revealing that there are permissible thresholds for diarrhea-causing parasites derived from fecal matter in water supplies.
9. Anabaena sp.
Anabaena circinalis, a visually intriguing cyanobacteria, thrives in freshwater reservoirs globally, including regions like Australia, Europe, Asia, New Zealand, and North America. These cyanobacteria are considered among the earliest multicellular organisms on Earth, having developed unique survival mechanisms. Anabaena spp., for instance, are known for producing neurotoxins. The identification of Anatoxin-a marked a significant discovery as one of the first neurotoxins produced by cyanobacteria. This discovery was underscored by a major outbreak in the 1950s, where contaminated drinking water led to widespread cattle fatalities across the United States.
In Australia, certain strains of freshwater Anabaena bacteria have been found to produce saxitoxins, potent neurotoxins that can lead to respiratory failure and subsequent death. The severity of these toxins has led to their classification as Schedule 1 substances by the military, indicating their primary utility in weaponry. On a positive note, cyanobacteria are relatively easier to filter out from drinking water, at least for the time being.
8. Rotifers
Rotifers are ubiquitous microorganisms found across the globe and are among the most frequent contaminants in drinking water. Despite their size, which can reach up to 1mm—visible to the naked eye—they are generally harmless to humans. These organisms exhibit diverse movements; some swim, while others move in an inchworm-like fashion. Interestingly, they are frequently detected in tap water, appearing fairly often.
The presence of rotifers in municipal water systems often signals issues with filtration, as organisms of their size should not penetrate such systems. Additionally, rotifers can serve as carriers for protozoans, such as cryptosporidium, and bacteria. This dual role offers a paradoxical advantage: while their presence alerts officials to potential system failures, it also indicates that other harmful contaminants might have already breached the filtration process.
7. Copepods
The previous entry referenced a Connecticut public health bulletin designed to inform residents about tiny organisms occasionally found in tap water. It highlights two near-microscopic invertebrates: rotifers and copepods. Copepods, the larger of the two, are a type of crustacean resembling miniature shrimp and are incredibly widespread, appearing everywhere. They can grow up to 2mm, twice the size of rotifers.
During a 2009 incident in Connecticut, residents discovered thousands of copepods in small water samples. One individual described them as “tiny polliwogs,” expressing disgust: “It was completely disgusting. We were drinking them, washing our clothes in them, and it was just completely nasty.” Despite their unsettling presence, copepods can be beneficial as they often consume toxins. However, their ability to bypass filtration systems suggests that smaller, potentially harmful bacteria might also infiltrate the water supply.
6. E. Coli
E. coli, or Escherichia coli, is a well-known bacterium associated with fecal matter, gaining widespread attention to the point of becoming infamous in the microbial world. It is pervasive, found in food, water, and even more food, making it nearly unavoidable. This makes it unsettling to learn that all drinking water contains trace amounts of E. coli, albeit maintained at levels deemed “safe.”
The Environmental Protection Agency (EPA) provides a data sheet on drinking water contaminants, which states that E. coli is permissible as long as it does not exceed 5 percent of the monthly water samples tested. For instance, if a municipality conducts 100 tests in a month, up to 5 samples can contain E. coli without violating safety standards. At microscopic levels, it is almost certain that some E. coli will always be present in water supplies.
5. Rhizopus stolonifer
In nature, vibrant colors often signify something intriguing, but this logic falters when applied to mycotoxic mold spores. While they might seem fascinating, their presence in drinking water is problematic. Rhizopus stolonifer, commonly known as black bread mold, is one such organism. It thrives on exposed bread, among other surfaces, and can become a significant issue if it contaminates water supplies.
As the most prevalent fungus globally, it’s no shock that this mold also appears in tap water. Fungi reproduce via spores, which, similar to flower pollen, drift through the air until they land in a suitable environment. A 2006 study examined mold spore concentrations in tap water and found Rhizopus stolonifer present 2.9 percent of the time—a relatively low rate compared to other contaminants (E. coli, for instance, is legally allowed at nearly double this frequency). While it is thought to release harmful toxins, these are only dangerous at higher concentrations.
4. Naegleria fowleri
This organism may not appear as frightening as others on this list—resembling mere mold splotches—but it is, in fact, a brain-eating amoeba. Scientifically speaking, it invades the nervous system through nasal passages, proving fatal to 98 percent of its victims.
Infections from N. fowleri are rare, primarily because ingestion doesn’t lead to infection. However, in 2011, two Louisiana residents died from meningoencephalitis (caused by Naegleria) after using a nasal rinse made from salt and tap water. Investigations revealed the amoeba on bathtubs, showerheads, and sink faucets—essentially covering the house. Despite this case, most infections occur from swimming in lakes and rivers. Ever accidentally inhaled water through your nose while swimming?
3. Salmonella Enterica
From a young age, we’re taught to cook chicken thoroughly and wash our hands after handling raw poultry. The reason behind this is salmonella, a bacterium with a long history of causing infections. While it’s commonly associated with foods like beef, spinach, and chicken (hedgehogs too, surprisingly), it can also contaminate drinking water, leading to outbreaks.
In 2008, Colorado’s tap water was linked to 79 cases of salmonella poisoning, resulting in symptoms like fever and vomiting. Vulnerable populations, such as the elderly, are particularly at risk. A study in Togo, Africa, identified 26 instances of salmonella in the water supply, highlighting the heightened risk in developing nations. While it’s logical, having concrete data helps pinpoint the sources of waterborne illnesses in these regions.
As Benjamin Franklin famously said, “In wine there is wisdom, in beer there is freedom, in water there is bacteria.” We’ll stick with the wine.
2. Chaetomium sp.
This mold species appears more intimidating than the colorful variety in number five. Similar to black bread mold, Chaetomium is commonly found in damp environments, ranging from swamps to bathroom ceilings. While it rarely contaminates tap water, its presence can cause the water to develop an unusual taste and odor—clear indicators to avoid consuming it.
Chaetomium spores are generally not harmful, though they can occasionally lead to an infection called phaeohyphomycosis—something best left unsearched online. They may also pose risks to individuals with spore allergies, particularly after prolonged exposure.
1. Legionella Pneumophila
The name Legionella alone evokes a sense of danger, and rightly so. This bacterium earned its name after an outbreak at an American Legion convention in 1976, which resulted in 34 deaths and 221 infections. The illness it causes, now known as Legionnaires’ disease, hospitalizes approximately 18,000 people annually. The source? Contaminated water. Symptoms include confusion, high fevers reaching 107°F (41.5°C), loss of coordination, vomiting, diarrhea, and muscle pain. Outbreaks can be sudden and widespread, such as the 2001 incident in Spain where over 700 people were infected in a single area.
If Legionella pneumophila wasn’t already formidable, the U.S. military attempted to weaponize it, creating a genetically modified strain with a 100 percent kill rate. Even if you’re not a target of such experiments, it’s wise to exercise caution around water in general.
