Think Before you Drink- Part 1 – Viruses and Bacteria in Tap Water

Although 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 make their way into untreated drinking water, causing various illnesses in people, mainly children, which cause 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, in 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 that affects the intestines, is spread through feces, and is deadly in HIV/AIDS patients. Oocysts are thick-walled and resistant molecules that 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 into our drinking water but never actually cause us harm unless the person drinking the water is a child or an elderly person, both of whom 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 the 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 waterborne illnesses (1). Rotaviruses have been found in chlorinated drinking water (1). Both hepatitis . A and rotaviruses are the likeliest causes of traveler’s diarrhea. A review listed 110 different virus types that are capable of environmental transmission, including the 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 the selection of certain resistant bacteria, there is also pressure on pathogens to survive our water treatment strategies. Certain pathogens respond to treatments by going into a shell-like state, which makes them undetectable in water supplies but allows them to still retain their virulence, allowing them to affect the host if ingested. Bacteria have shown the ability to enter and grow inside protozoa, which gives them protection from disinfection. Bacteria are also capable of entering 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 system (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 that goes through pores in our eyes are other methods by which 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 to each other (biofilms in drinking water and their role as reservoirs for pathogens).

Experiments have shown that many viruses have the potential to persist in and be released from biofilms in the water system (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 medium 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 and 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 waterborne illness come from private or groundwater source wells that were not properly disinfected.

Discussion

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 disinfection 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 sick 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!

Sources

1. Szewzyk, U., Szewzyk, R., Manz, W., & Schleifer, K. H. (2000). Microbiological safety of drinking water.Annual Reviews in Microbiology, 54(1), 81-127.
2. http://www.cdc.gov/parasites/glossary.html
3. Ford, T. E. (1999). Microbiological safety of drinking water: United States and global perspectives.Environmental Health Perspectives, 107(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 microbiology, 47(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 health, 214(6), 417-423.
6. Ford, T. E. (1999). Microbiological safety of drinking water: United States and global perspectives.Environmental Health Perspectives, 107(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 microbiology, 73(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 microbiology, 85(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.
10. http://www.cdc.gov/healthywater/drinking/public/water_treatment.html
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.