Warning: This list is not for the faint of heart. There are invisible monsters living in your tap water, creatures that swim and multiply by the billions inside every drop of brisk, refreshing water you slurp down your gullet, tiny demons that…well, okay, they’re actually not all that bad. All water has bacteria and protozoans to some extent, most of them completely harmless. But once you see what they look like up close and personal, you might never get the image out of your head. Here are 10 microorganisms that could be living in your drinking water right now.

When cities pump water out to their residents, they put the water through a series of filtration and disinfection steps first. This is obviously beneficial because when you pull water from lakes and rivers it’s most likely going to be filled with bacteria. Filter it, and you can get most of that bacteria out. The important word there is “most,” because even the most advanced filtration techniques are not infallible. And for many people, that means drinking tiny doses of cryptosporidium every day.

Cryptosporisium is what’s known as a protozoan—a single-celled organism—and is most famous for giving people bouts of crippling diarrhea, a condition affectionately referred to as cryptosporidiosis. The protozoa works like a parasite, latching onto the intestines and laying eggs in a person’s fecal matter—and that’s how it spreads: when drinking water becomes contaminated with infected fecal matter, crypto moves on to new hosts. We have safeguards in place to stop it from happening, but on a good day it only stops 99 percent of the cryptosporidium. In 1998 a crypto bloom broke out in Sydney, Australia. Officials noticed the rise, but didn’t act for a few days because the levels were still “within acceptable health limits.” That means that there are acceptable levels for a diarrhea-inducing parasite that comes from poop in your water.

This pleasant looking slinky is Anabaena circinalis, a cyanobacteria that lives in freshwater reservoirs around the world, notably Australia, Europe, Asia, New Zealand, and North America. Cyanobacteria like this are believed to be some of the first multicellular organisms on earth, and as such have evolved to do some very curious things. In the case of Anabaena spp., those things are the production of neurotoxins. The discovery of Anatoxin-a was one of the first cases of a neurotoxin being produced by cyanobacteria, and we found out in a big way: An outbreak in the 1950’s got into the drinking water supply and was responsible for a series of mass die-offs at cattle farms across the U.S.

In Australia, freshwater Anabaena bacteria have been found producing saxitoxins, a type of neurotoxin that causes respiratory arrest, followed by death. The military has even gone so far as to classify saxitoxins as Schedule 1 substances with “no practical use outside of weapons manufacture.” Fortunately, cyanobacteria are one of the easier microorganisms to filter out of drinking water. For now.

Rotifers are a relatively common microorganism that can be found pretty much everywhere in the world. And they’re also one of the most common drinking water contaminants, despite growing as large as 1mm at times (which is hardly microscopic—you can see that with your naked eye). Some of them swim, others crawl around with an inchworm motion, but none of them are known to be harmful to humans. And that’s good, because they show up in tap water fairly often.

What’s not good is that the presence of rotifers in a municipal water supply usually means that there is a problem with the filtration system—organisms that large should not be able to make it through. And rotifers are also known to act as hosts to protozoans (like cryptosporidium) and bacteria. That leads to a mirrored benefit, of sorts: rotifers can be used as a warning system to let officials know that there’s something wrong with their systems, but by the time they’re seen, there could be other things that got through as well.

The link in the previous entry pointed to a Connecticut public health bulletin meant to advise residents who might find tiny bugs swimming around in their tap water. It addresses two types of near-microscopic invertebrates: rotifers, and copepods. Of the two, copepods are larger, and possibly even more common. They can grow up to 2mm (double the size of rotifers), and they’re actually a type of crustacean, sort of like miniature shrimp. And they’re everywhere.

In the Connecticut incident, which happened in 2009, residents began finding thousands of them in small samples of water. One resident compared them to “tiny polliwogs,” and stated, “It was completely disgusting. We were drinking them, washing out clothes in them, and it was just completely nasty.” But if anything, copepods are beneficial because they often feed on toxins. Again though, the fact that they can make it through the filtration system means plenty of smaller bacteria can too.

We all know about E. coli, or Escherichia coli, a bacteria that lives in, on, and around fecal matter. It’s been publicized more times than you can shake a stick at, until by now it’s practically a legend of the bacteria world. From food to water to even more food, it’s hard to get away from. Which is why it’s sort of disconcerting to find out that all drinking water invariably has E. coli in it; it’s just kept down to levels that are considered “safe.”

Here’s the data sheet on drinking water contaminants from the Environmental Protection Agency, or EPA, of the United States. According to that sheet, E. coli is acceptable as long as it doesn’t appear in more than 5 percent of the water samples collected in a given month. So if the municipality tests their water 100 times in a month, 5 of those samples can be infected with E. coli, but the water will still be permitted to go out to the city’s residents. And once you get down to decimal places of hundredths or thousandths of a percent, you are pretty much always guaranteed to find some E. coli swimming and playing in your water.

In the world at large, the more colorful something is, the more fun you can probably have with it. And based on that logic, these mycotoxic mold spores are just a big barrel of laughs. Until they start showing up in drinking water; then you have problems. Rhizopus stolonifer is more commonly known as black bread mold; leave a piece of bread out in the open, and this will be just one of the molds that take over it.

Widely considered the most common fungus in the world, it’s not surprising that this mold shows up in tap water as well. Fungi reproduce with spores which, much like flower pollen, float through the air until they find a suitable place to land and grow. In 2006, a study looked at the concentrations of mold spores in tap water, and found that Rhizopus stolonifer appeared 2.9 percent of the time, which, arguably, is fairly low in the realm of contaminants (remember, E. coli can legally show up nearly twice as often). It’s believed to release toxins that are harmful to humans, although they’re only dangerous in higher concentrations.

This organism doesn’t look as terrifying as some of the other creatures on this list—really it just looks like a few mold splotches. It’s actually an amoeba, though, and it eats brains. To be scientific about it, the amoeba attacks a person’s nervous system by entering through their nasal cavities, killing 98 percent of its victims.

N. fowleri infections are rare, mostly because it isn’t effective if it’s consumed orally. But in 2011, two Louisiana residents died from meningoencephalitis (the disease caused by Naegleria) after making a nasal flush out of salt and tap water. When the deaths were investigated, the brain eating amoeba was found on the bathtub, shower heads, and sink faucets—the house was literally covered in it. Despite this case, most infections aren’t caused by tap water infected with N. fowleri. No, usually people get it by swimming in lakes and rivers. Have you ever accidentally sucked water up your nose while swimming?

With a name like Legionella, this bacteria already sounds dangerous. And since it was named after an American Legion convention in 1976 where it was responsible for 34 deaths and a total of 221 infections, that might be a fair assumption. The condition caused by L. pneumophila is now called Legionnaires’ disease, and it sends 18,000 people to the hospital every year. And it comes from, you guessed it, contaminated water. Symptoms of Legionnaires’ disease include confusion, fevers of up to 107 F (41.5 C), loss of coordination, vomiting, diarrhea, and muscle aches. It shows up sporadically; in 2001, more than 700 people in Spain were infected in one centralized area.

As if L. pneumophila wasn’t already dangerous enough, the U.S. military decided to take a crack at weaponizing it, leading to a genetically modified version with a 100 percent kill rate. But even if you’re not on a government hit list, you would do well to stay away from water in general.

Here’s another type of mold, and one that looks slightly more terrifying than the psychedelic funhouse in number five. Like black bread mold, Chaetomium species are fairly common in everyday life, usually floating through the air in moist locations, which can encompass everything from a swamp to your bathroom ceilings. This appears in tap water fairly rarely, but when it is there it usually makes the water taste and smell slightly “off”—normal signs to stop drinking a glass of water in any case.

Chaetomium sp. spores aren’t particularly dangerous, although in some cases they can cause an infection known as phaeohyphomycosis, which is something you definitely do not want to Google. They can also present a hazard to people who are allergic to the spores, and even that typically only happens with chronic exposure.

One of the first things we learn as children is that you always cook chicken, and if you handle it raw you better scrub those hands nice and good. The reason, of course, is salmonella, which has such a long history of infection it’s not even possible to link to them all here. Usually salmonella shows up on food such as beef, spinach, and of course, chicken (hedgehogs too, surprisingly). Less commonly, salmonella causes outbreaks through none other than our friendly neighborhood drinking water.

In 2008, Colorado tap water was responsible for 79 cases of salmonella poisoning, which caused fevers and vomiting. People with weak immune systems, like the elderly, are especially susceptible to salmonella. Another study looked at the water supply of Togo, Africa, and found 26 cases of salmonella contamination, suggesting that developing countries are at a greater risk for bacterial infections from drinking water. It’s sort of common sense, but it’s beneficial to have figures to see what exactly is causing illnesses in these areas.

As Benjamin Franklin once said, “In wine there is wisdom, in beer there is freedom, in water there is bacteria.” We’ll take the wine.

It is weird to think that diseases can be used to cure other diseases. However, it is true. For centuries, scientists have figured out ways of using deadly, pathoegenic bacteria, viruses, and protozoa to cure deadly diseases caused by other pathogens.

It may seem counterintuitive to cure one illness with another, but it has worked time and time again. And it’s not always that scary. Other microorganisms, specifically viruses and bacteria that are not necessarily dangerous to humans, have also been utilized to treat lethal diseases.

10 Malaria

Syphilis was incurable throughout most of history and often led to death within four years. The worst form is neurosyphilis, which is infection of the nervous system by syphilis and often the final stage of the disease. Neurosyphilis is accompanied by blindness, madness, paralysis, and, subsequently, death. Most syphilis patients were confined to asylums until they died.

Austrian psychiatrist Dr. Julius Wagner-Jauregg started developing a treatment for syphilis in the 1880s. He turned to pyrotherapy—the artificial induction of a fever, in this case by the introduction of a more manageable pathogen. The high fever caused by the introduced infection kills off the incurable disease, and the curable disease is treated thereafter.

Dr. Wagner-Jauregg unsuccessfully tried using tuberculosis antigen as well as the typhus and typhoid vaccines to cure syphilis. However, he got his break in June 1917, when a wounded soldier suffering from malaria was sent to the psychiatric ward of the hospital where he worked. This was clearly an error because the soldier had no mental issues. But the doctor seized the opportunity to work on his pyrotherapy treatment for syphilis.

Dr. Wagner-Jauregg extracted blood from the soldier and injected it into nine people suffering from advanced syphilis. The malaria-causing Plasmodium protozoa caused a serious fever that killed off the syphilis-causing Treponema pallidum bacteria. Dr. Wagner-Jauregg went on to cure the six survivors—who now had malaria—with quinine.

Dr. Wagner-Jauregg published his findings in 1918. He noted that syphilis is killed when the body maintains a temperature of 41 degrees Celsius (106 °F) for six hours. His treatment soon became the method of choice for syphilis. However, it had its downsides, even though it was considered successful.

Syphilis patients often suffered from complications when they were injected with a different blood type. They also inherited the blood diseases of their donors. The deadly malaria strain used at the time could also cause anemia and kidney failure. Doctors later switched to the less deadly Plasmodium vivax strain. This method of treatment was abandoned after the advent of antibiotics.^[1]     

9 HIV

It is especially surprising that one of the world’s worst diseases can be used to treat other deadly ailments. Scientists have discovered a way to use HIV to cure leukodystrophy and Wiskott-Aldrich syndrome, two deadly diseases that often affect children.

To be clear, we do not use HIV itself but viral vectors created in part from HIV. A viral vector is used to deliver genetic material into cells, as in gene therapy. In 2010, a team of Italian doctors led by Dr. Luigi Naldini injected 16 children with HIV-based viral vectors. Six had Wiskott-Aldrich syndrome, while the other ten suffered from leukodystrophy.

Three years later, they observed that six of the children were slowly recovering from the diseases. Three suffered from Wiskott-Aldrich syndrome, and the other three suffered from leukodystrophy.^[2] The other ten were also showing some signs of recovery. The procedure is inconclusive because it is still undergoing clinical trials.

8 Cancer

CRISPR (pronounced “crisper”) means “Clustered Regularly Interspaced Short Palindromic Repeats.” It is used in the CRISPR-Cas9 gene editing technology that allows scientists edit the DNA in cells.

While scientists concentrate on using CRISPR to modify unfavorable genes, researchers at the Rutgers Cancer Institute of New Jersey are trying to use it to cure cancer. CRISPR works for cancer treatment because cancerous cells roaming in the body tend to circulate back to the tumor they originated from.

Using CRISPR technology, researchers at the Rutgers Cancer Institute injected these cancerous cells with the cancer-killing S-TRAIL protein. The S-TRAIL-containing cancerous cells killed other cancerous cells in the tumors when they entered them. Then they essentially self-destructed thereafter. The technology has not been tested on humans, though, and experiments have been confined to mice.^[4]

7 Cowpox

The cowpox virus was used to create the first vaccine for smallpox, a lethal virus that infected millions of people until it was declared eradicated in 1977. The cowpox vaccine is the reason vaccines are called vaccines. The name was derived from vaccinus, the Latin word for “cow.”

While we credit England’s Dr. Edward Jenner for creating the first smallpox vaccine, we know ancient Chinese and Middle Easterners deliberately infected themselves with cowpox to make themselves immune to the virus for centuries.

Dr. Jenner created the smallpox vaccine after observing that milkmaids never contracted smallpox. He later realized this was because they had been infected by cowpox—a closely related virus—from the cows they milked. Dr. Jenner proved his theory right in 1796, when he deliberately infected eight-year-old James Phipps with cowpox.

Dr. Jenner infected Phipps with smallpox a month and a half after infecting him with cowpox. Phipps never developed smallpox, indicating that he was immune to the virus. Dr. Jenner later published his findings. The smallpox vaccine which later eradicated the disease was derived from the vaccinia virus, another closely related virus.^[4]

6 Poliovirus

Poliovirus causes polio, which used to be one of the deadliest diseases out there. Fortunately, it is on the brink of extinction today. Only 22 incidents of polio were reported in 2017, which is a far cry from the 350,000 cases reported in 1988.

Interestingly, scientists are developing a method of using the once-deadly disease to cure glioblastoma (GBM), a rare but deadly and highly aggressive form of brain cancer. Glioblastoma is treated with surgery, radiation, and chemotherapy. However, it often returns and kills the patient within about a year.

The poliovirus therapy was developed by researchers from Duke Cancer Institute, Durham, North Carolina. They genetically modified the poliovirus to create a new virus called PVSRIPO, which is injected right into the brain tumors caused by glioblastoma.

A clinical trial conducted on 61 glioblastoma patients indicated a 21-percent survival rate. That seems small until we realize that patients given the standard treatments have a survival rate of just four percent.

While PVSRIPO looks promising, it could cause some unfavorable side effects depending on the location of the tumor in the brain.^[5]

5 Bacteriophage Therapy

In 2015, 69-year-old Tom Patterson was diagnosed with pancreatitis (inflammation of the pancreas) while visiting Egypt with his wife. Conventional treatment did not work, and he was later flown to Frankfurt, Germany. Doctors drained the fluid around his pancreas to discover he was infected with drug-resistant Acinetobacter baumannii bacteria.

Patterson was later flown to Thornton Hospital, San Diego, California, where a drain was inserted around his pancreas to control the dripping. Unfortunately, the drain slipped, and the fluid leaked into his abdomen and bloodstream. Patterson soon started experiencing high fever, serious pains, and breathing difficulties. He also fell into a coma that lasted for about two months.

Doctors settled for bacteriophage therapy as a last-ditch effort to save his life. Unlike what the name suggests, bacteriophages are viruses and not bacteria. The name means “bacteria eater” and refers to a distinct class of viruses that attack bacteria. Every bacterium has a bacteriophage that has evolved to use it to replicate.

Bacteriophage therapy refers to the use of these bacteria-attacking viruses to cure bacterial infections. It was the go-to method of dealing with deadly bacteria until antibiotics came along. However, its results are not scientifically proven.

Nevertheless, the therapy worked, and Patterson was slowly recovering from the coma—until the A. baumannii bacteria mutated and developed resistance against the virus. Doctors solved this problem by passing a newer strain of the virus into Patterson’s body until he was finally cured.^[6]

4 Maraba Virus

Scientists have always known that the Maraba virus (aka MG1 virus) attacks and destroys cancer cells. However, scientists at the Ottawa Hospital and the University of Ottawa have discovered that the Maraba virus also attacks and destroys HIV-infected cells.

HIV works by infecting and rapidly multiplying in the immune system cells of its hosts. However, some HIV-infected cells turn dormant after some time, while others continue to reproduce.

Doctors often administer antiretroviral drugs to suppress HIV. However, the drugs only work on active HIV-infected cells and have no effect on the dormant cells. The dormant cells kick into action and begin to rapidly reproduce when the patient stops taking the antiretroviral drugs.

Lab tests have proven that the Maraba virus will destroy dormant HIV-infected cells, indicating a possible cure for HIV. However, the procedure is considered inconclusive since tests have only been conducted in the lab, and this method has not been tested on animals or humans.^[7]
 

3 Coley’s Toxin Treatment

Coley’s toxin treatment involves use of bacteria to treat cancer. The procedure is named after William Coley, a New York bone surgeon who developed it in the 1890s. Coley invented the treatment after observing that patients who get infected with bacterial diseases while recovering from cancer surgeries were often better off than uninfected patients.

Coley believed this happened because the bacterial infection strengthened the patient’s immune system. So he began injecting live bacteria into his cancer patients. He later switched to using dead bacteria, given that live bacteria could still cause deadly infections.

Scientists do not agree on how the process works. Some think the injected bacteria strengthen the immune system against cancer cells. Others think the bacteria actually encourage the production of either a protein called interleukin 12 (IL12) or tumor necrosis factor (TNF) proteins that fight cancerous cells. Another group think it’s high fever that kills the cancerous cells, just like the pyrotherapy procedure we mentioned earlier.

Nevertheless, Coley’s toxin treatment had mixed results. It worked with some patients but did not work with others. However, it was widely used until the early 1950s, when it was displaced by other cancer treatments like chemotherapy. An improved version utilizing genetically modified bacteria is still used today.^[8]

2 Predatory Bacteria

Predatory bacteria are those that attack and eat other microorganisms. Predatory bacteria work by attacking and breaching the walls of enemy bacteria cells. Once inside, it eats the bacterium’s innards before reproducing and leaving to attack other, similar bacteria cells.

Scientists are already working on using predatory bacteria to treat other bacterial infections, especially superbugs that have become immune to regular antibiotics.

In November 2016, the BBC reported that scientists at Imperial College London and the University of Nottingham had successfully used the Bdellovibrio bacteriovorus predatory bacteria to kill Shigella, a deadly genus of bacteria that causes food poisoning and kills over a million people a year.

Scientists observed Shigella populations reduce by 4,000 times after exposure to B. bacteriovorus in the lab. Another test in fish larvae saw the survival rate of the larvae infected with Shigella increase from 25 percent to 60 percent. Scientists plan on testing B. bacteriovorus on other deadly human bacteria, including Salmonella and E. coli.^[9]  

1 CAR-T Therapy

T-cells play a vital role in the body’s immune system. Recently, scientists have developed a method of using the T-cells to create chimeric antigen receptor T-cell therapy (CAR-T therapy), an anticancer treatment.

CAR-T therapy works by extracting the natural T-cells in the body and programming them with chimeric antigen receptors, which greatly improve their ability to detect, bind to, and destroy cancerous cells. The genetically modified T-cells are tailored to target the specific cancer affecting the patient, making them the perfect cancer cell assassins.

However, CAR-T therapy is only used as an option of last resort because it can cause a myriad of side effects, including brain inflammation. The process is also time-consuming, since the T-cells need to be tailored to the patient. The entire procedure could take four months.^[10]