Think before you drink- Part 1 – Viruses and bacteria in tap water


sink-334347_1280Although drinking water in the United States is treated with chemicals to kill bacteria and viruses, reaching complete sterilization of the water is impossible. Instead the government sets safe limits for each virus and bacteria, meaning that an amount of contamination at or below the limit is unlikely to result in any sickness or harm to the individual. How this limit is determined is complex and will not be discussed here.

According to the World Health Organization (WHO) 300,000 children die each year from diarrhea, mostly caused by unsafe drinking water. Bacteria and viruses contained in feces from humans and animals makes its way into untreated drinking water causing various illnesses in people, mainly children, which causes diarrhea and eventually death. As some of you have probably traveled to various developing countries you can attest to getting traveler’s diarrhea from consuming contaminated drinking water. Luckily tap water in the United States is some of the safest in the world and is nearly devoid of harmful microorganisms although some persist.

I will give one example showing the serious effects an illness traveling through a water system can have. In 1919 Germany there was a typhoid fever outbreak linked to contaminated water that caused 4,000 cases of typhoid fever and 400 deaths (1). It was proven that the water was contaminated by sanitary waste used as fertilizer on a frozen agricultural field. Obviously today even if the illness got into the water systems, the treatment methods we have would destroy it pretty quickly. I am just mentioning this instance to show that it is possible for pathogens to travel through water and make us sick if there is some contamination or problem with our water systems which prevents our methods from completely destroying all potentially dangerous pathogens. Highly unlikely, but still possible.

Water contamination in the United States

According to the Center for Disease Control (CDC) and the U.S. Environmental Protection Agency in 1994 about 400,000 people became sick from drinking water contaminated with Cryptosporidium oocysts that passed through the water plant filtration systems. Cryptosporidiosis is a parasitic disease which affects the intestines, is spread through feces and is deadly in Aids patients. Oocysts are thick walled and resistant molecules which are shed in the feces of those with a sickness, in this case Cryptosporidiosis (2). Once these oocysts reach their target (human intestines) they infect the host with the parasitic disease.

It is estimated that a few thousand people a year get sick from pathogens in tap water. This is probably a large underestimate of the actual number of illnesses because: some people become infected but display no symptoms, they get sick but do not get treatment, and sometimes treatment is sought but doctors do not report the illness (3). A study by Payment in Canada found that about 35% of the reported Gastro Intestinal illnesses reported by tap water drinkers were water-related and preventable (3). It is possible that more pathogens make their way to our drinking water but never actually cause us harm unless the person drinking the water is a child or an elderly person which both have vulnerable immune systems.

Bacteria in tap water

One bacteria indicative of poor water quality is a bacterium many of you have heard of- E coli. E coli made the news when McDonald’s customers got sick from eating infected beef.  E coli is commonly found in feces, so if water tested has E. coli, there is a high chance that the water has been contaminated with feces and may contain other bacteria commonly found in feces such as Shigella and Salmonella spp.

All of these bacteria commonly found in feces likely infect water through agricultural runoff or directly from domestic or wildlife animal feces (1) E. coli can affect drinking water when repairs are being performed on the distribution system pipelines or when contaminated surface cattle manure runoffs into well water (4).

Viruses in tap water

Viral pathogens in drinking water may be the scariest of all pathogens. There is evidence showing that hepatitis A and rotaviruses are recurrent causes of water borne illnesses (1).  Rotaviruses have been found in chlorinated drinking water (1). Both hep. A and rotaviruses are the likeliest cause of traveler’s diarrhea.  A review listed 110 different virus types that are capable of environmental transmission including Norwalk virus, poliovirus, adenovirus and astrovirus, among others (4). Just because these viruses are capable of being transmitted in water does not mean they will-they are most likely killed off with water treatment procedures.

Like our evolving treatment strategies, viruses and bacteria are also evolving methods to survive most of our attempts to destroy them. Similar to my blog talking about pressure from antibiotics causing selection of certain resistant bacteria, there is also a pressure on pathogens to survive our water treatment strategies (1 Certain pathogens respond to treatments by going into a shell like state which makes it undetectable in water supplies but allows it to still retain its virulence allowing it to affect the host if ingested (1 Bacteria have shown the ability to enter and grow inside protozoan which give them protection from disinfection (1 Bacteria are also capable of entering inside treatment resistant cysts produced by protozoa.

Enteroviruses, mainly excreted in the feces of infected individuals, can affect organ systems like the liver (Hepatitis A and E viruses), cause gastrointestinal illnesses (noroviruses and rota viruses), or affect the central nervous sytem (polio virus) (5).

Water from hot water heaters

Water coming from hot water heaters may contain pathogens as this warm water is an ideal environment for many pathogens. While we usually do not drink warm water, warm shower water that we swallow or which goes through pores in our eyes are other methods where these pathogens may enter our bodies. I will go into much greater detail on this topic in the future.

Biofilms- How pathogens survive inside pipes

Although the sanitation process kills almost all of the bacteria and viruses some survive but cannot multiply, while others are able to survive and multiply, mainly in biofilms (6). Biofilms are groups of microorganisms that stick to each other on a surface, in this case water pipes. Organisms gathered as biofilm tend to be more resistant to environmental stress such as heavy metals, starvation and chlorine (7). In the lab E. coli has shown the ability to multiply in biofilm (7).

One study found that H. pylori- the bacteria responsible for peptic ulcers, was able to survive in a viable state in mixed species heterotrophic biofilms in the water distribution systems (8). The microorganisms making up the biofilm communicate with and transfer genes with each other (biofilms in drinking water and their role as reservoir for pathogens).

Experiments have shown that many viruses have the potential to persist in and be released from biofilms in the water systems (5). A study from Germany found Legionella spp. and Pseudomonas aeruginosa in biofilms but did not find any enterococci bacteria (8).

Detection of viruses and bacteria in water

When microorganisms are under stressful conditions (such as during water disinfection methods) or have limited nutrients they are capable of going into a viable but non-culturable (VBNC) state; this means that they do not grow on a media they normally grow on in laboratory tests, yet they are still alive and become culturable again when more favorable conditions become present (5). This would lead scientists to estimate that no viable microorganisms are present in a water sample.  Another issue is that laboratories use a very specific strain of a virus or bacteria that may differ from a similar virus or bacteria found in its natural environment (9).

Water Treatment in the United States

In most public water systems surface water (lakes, rivers) is used (as opposed to underground water as in wells). The first step in the treatment process involves releasing chemicals with charges into the water to bind with other chemicals and dirt to form larger particles called floc.  Once the flog settles to the bottom of the water, the clear water on top passes through various filters-sand, gravel and charcoal- to remove dust, parasites, bacteria, viruses and chemicals. The filtered water is then treated with a disinfectant (chlorine, chloramine are the most common) to kill any leftover bacteria, parasites and viruses (10). Our treatment methods are extremely effective and kill nearly all viruses and bacteria.

Well water

Wells in rural areas have a much higher chance of pathogenic infestation than the public water systems maintained by the government in urban areas. In the United States at least 30% of the rural wells are contaminated with feces and exceed the current government standards for safe drinking water (11). The CDC (Center for Disease Control) monitors water borne illnesses each year. Almost all of the cases of water borne illness come from private or ground water source wells that were not properly disinfected.


The United States has some of the cleanest drinking water in the world. This is not to say that it is perfect. Our public water systems are extremely old and because of this sometimes the treatment method does not work exactly as intended and some pathogens survive in the piping. Fortunately, this is extremely rare. I am confident in saying that about 99.9% of all viruses and bacteria that make their way into our water system are destroyed before they reach your house.

With the exception of the large outbreak in Milwaukee, only a few thousand people a year get sick from pathogens in tap water. And these cases are usually from untreated well water. It is possible that many more get sick each year but never go to the doctor or never link their illness to tap water consumption but the number is still low. Although biofilms are a place for pathogens to gather, once they are released into the water again they should be killed by the disinfectant process so they likely will never reach your tap.

On those rare occasions that pathogens do make it into your glass of water, it is unlikely that you will even get sick. Populations such as children and the elderly which are more vulnerable to this may get very ill. Tap water used in hospitals should also be monitored closely as any pathogen has the potential to cause serious illness in sickly hospital patients.

So, this means tap water is safe to drink eh? Well, in regards to bacteria and viruses, sure. But tap water contains many chemicals, pesticides, pharmaceuticals and animal runoff which can present serious health problems including cancer. But these are topics for other blogs in the near future!


  1. Szewzyk, U., Szewzyk, R., Manz, W., & Schleifer, K. H. (2000). Microbiological safety of drinking water.Annual Reviews in Microbiology54(1), 81-127.
  3. Ford, T. E. (1999). Microbiological safety of drinking water: United States and global perspectives.Environmental Health Perspectives107(Suppl 1), 191.
  4. Keswick, B. H., Gerba, C. P., DuPont, H. L., & Rose, J. B. (1984). Detection of enteric viruses in treated drinking water.Applied and environmental microbiology47(6), 1290-1294.
  5. Wingender, J., & Flemming, H. C. (2011). Biofilms in drinking water and their role as reservoir for pathogens.International journal of hygiene and environmental health214(6), 417-423.
  6. Ford, T. E. (1999). Microbiological safety of drinking water: United States and global perspectives.Environmental Health Perspectives107(Suppl 1), 191.
  7. Juhna, T., Birzniece, D., Larsson, S., Zulenkovs, D., Sharipo, A., Azevedo, N. F., … & Keevil, C. W. (2007). Detection of Escherichia coli in biofilms from pipe samples and coupons in drinking water distribution networks.Applied and environmental microbiology73(22), 7456-7464.
  8. Mackay, W. G., Gribbon, L. T., Barer, M. R., & Reid, D. C. (1998). Biofilms in drinking water systems: a possible reservoir for Helicobacter pylori.Journal of applied microbiology85(S1), 52S-59S.
  9. Rusin, P. A., Rose, J. B., Haas, C. N., & Gerba, C. P. (1997). Risk assessment of opportunistic bacterial pathogens in drinking water. InReviews of environmental contamination and toxicology (pp. 57-83). Springer New York.
  11. Strauss, B., King, W., Ley, A., & Hoey, J. R. (2001). A prospective study of rural drinking water quality and acute gastrointestinal illness.BMC Public Health,1(1), 8.

12 thoughts on “Think before you drink- Part 1 – Viruses and bacteria in tap water

  1. Bernal Herrera

    In Latin America we don’t have water that can be drink provided by our services, we must use other sources like filter or big companies that provide bottled water.

    In my case we use at home Ozone filters, but I have also tried Osmosis filter that are quite good, although the “flavor” (if it can be said) of the water changes a little.

    Nice reading you again like every week and learning a lot !

    1. RobertRobert Post author

      So you have tap water that you filter? Is it normal for all house to have tap water? Various chemicals, minerals, etc. can change the flavor of the water. In my opinion distilled water is the purest. They collect the steam from water which leaves all of the bad stuff behind. I am actually not familiar with Ozone filters. I used a Brita filter in the past but they do not filter out fluoride so I went to bottled water.

  2. Kelli

    Do you personally drink tap water? Also, is it possible that we aren’t aware of the true number of water borne illnesses in the US? For example, when people exhibit symptoms like vomiting and diarrhea they tend to assume that it is from a stomach bug or the norovirus. Is it possible that it is actually from the water? I assume that most people do not go to the hospital for the run of the mill stomach bug so I’m sure it would be hard to find out if it’s actually from a parasite in your system or one from your tap…

    1. RobertRobert Post author

      I use tap water when I cook beans and soups, etc. but I normally do not drink tap water. I always have distilled water at home. Tap water always taste off to me. Probably the chemicals and minerals in it. Yes there are likely many more illnesses from tap water that are never reported. I would say a majority of the cases probably aren’t reported. People just assume its a stomach bug. But outside of gastro intestinal issues I do not think the tap water is doing any long term harm. At least in regards to bacteria/viruses. I will talk about other pollutants soon.

  3. Lucia Henkle

    At home there is always bottled water… distilled and spring water…. Personally I prefer spring water over distilled because of the flavor… Yes, I can feel the difference between waters (distilled & spring) and brands. Some spring bottled water flavors I don’t like and I try to avoid them.
    I started around 2 weeks ago to drink more distilled water at home, even if I don’t like the flavor; but at work I drink spring bottled water. And for example, if I ever go to a restaurant and they serve tap water I will drink it (Because I am almost sure the water they give is tap water). In other words, I will just drink any water… LOL… I will try to reduce my tap water intake.

    1. RobertRobert Post author

      Yes restaurants likely serve tap water. And dirty limes! I am actually not familiar with exactly how spring water is cleaned. I don’t think I mentioned in the blog but many times sewage leaks into above ground water sources like lakes and rivers. I did not mention this because nearly all of this is filtered or killed before it reaches our sinks. But if bottled water is taken from rivers that have high amounts of live bacteria and virsuses it is possible that it is less pure than tap water. Seems strange but they may have less stringent filtering methods than that required for tap water. I will have to look into this!

  4. Erica

    Makes you think twice about drinking tap water…does Brita filters or other similar types effectively change anything or make it safer/cleaner to drink?

    1. RobertRobert Post author

      hey erika. i am actually not sure how effective brita filters are. I would be interested in finding out. I will let you know when I write about it!

  5. Julio E. Henkle

    I am researching into your blog because last week we had a severe vomiting and diarrhea sickness in our family. Reading the newspaper we learned that more than 100 other cases were reported by a nearby hospital in this area. Many more cases were not attended by the hospital. We did not go to the hospital. After a complete diet for a full day, drinking some lemon juice, next day the symptoms subsided. We are O.K. now.
    Private Lab analysis indicate water had Noroviruses, Salmonella SP and Shigella. The city water company says their tests reveal no viruses or bacteria in the water they supply. The Ministery of Health is conducting more water tests. Even thou we drink only bottled water, the microorganisms probably got inside by the water used for cooking or brushing the teeth or taking a shower. After many years with no problems, suddenly something can happen and the tap water is not healthy enough.
    Congratulations! Your web site is very helpful. It has an attractive presentation, with beautiful related pictures, well organised into different themes, with very well documented health articles. I like your interest in nutrition-related research and the easy-reading way you write, how you experiment with the Vita-Mix in the kitchen and come up with new recipes. I also find meditation interesting and its philosophy of living the present, spreading kindness and being humble.
    I’ll be looking into some of the other articles in the blog that I find interesting, specially related to diet, disease management, physical activities, water, stress, lifestyle.

    1. RobertRobert Post author

      Hey Julio. Thanks for the nice comment. I am glad that you were only sick for a day. When I had a stomach virus it took me a few days to fully recover, and that was after going to the hospital. The Norovirus is pretty serious. I think that is what I had…about 25 people in my family got sick. I read a little about the Norovirus and why it is so contagious. The flu virus, which is considered contagious, requires about 45 flu particles to be inhaled for someone to become infected. The Norovirus is very contagious because it only takes 5 virus particles to become sick. Like you said, you probably got it from your tap water when you showered, brushed your teeth, washed your face, etc.

      I am glad that you find the website easy to read. There are some health topics that are complicated so it can be hard to write them in a way that anyone can understand, but I try my best. I could make my website a little more fancy but I honestly prefer the simplicity of it…it matches my outlook on life. If you ever have any more questions you can tell lucia, leave a comment or email me. I would be happy to hear your thoughts on other topics. Thanks again for the kind comment!

  6. Julio E. Henkle

    Are beverages such a Gatorade or Powerade better than water to improve the performance during sports activities?
    I have read articles stating both criteria.
    Yes, it improves because it replenishes your lost sodium electrolytes.
    No, the tests do not show any improvement.
    ¿What is the truth?

    Thank you
    Julio E. Henkle

    1. RobertRobert Post author

      Hi Julio. Whether or not you should drink water or Gatorade depends on how much you sweat. If you sweat for more than an hour I would recommend Gatorade to replace minerals lost in the sweat. Even so, I do not think it will increase your performance. It may give you more energy though since it is replacing lost electrolytes. Gatorade also has a lot of sugar, so unless you are burning a LOT of calories I would not drink more than a bottle of Gatorade. If you don’t eat a large meal and then bike for a long distance and just drink water you may become dizzy or light headed. That can obviously be dangerous if you are riding a bike. You can become dizzy by over working yourself, heat exhaustion, dehydration, etc. When I run during the summer heat I often feel like I am going to pass out. To prevent this, make sure that you stay hydrated while biking and avoid biking for long distances when it is really hot. I am not sure how hot it gets in Guatemala, but if it never gets above 70-75 degrees Celsius than you should not have a problem.

      So, I guess my final answer would be to drink water for shorter rides and Gatorade for longer rides, but the key is to drink something when exerting yourself.


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