[Pt.1] Bacteria Begone! Water Disinfection in Action!

Written by Kevin Liu | Edited by Josephine Chan

While looking at a chunk of snow or watching the rain pelt your windows from the insides of your home, you might be enjoying a warm cup of water. But the water in your cup and on the sidewalk are actually not very different. In fact, the water in your cup is just a purified version of the rain or snow outside, commonly referred to as “groundwater” since it seeps into the ground. All groundwater goes through an extensive purification process that filters out contaminants before adding chemical solutions to kill disease-causing pathogens [1]. This 20^th-century innovation was founded primarily based on chlorine’s bacteria-killing properties and has since been improved upon to ensure a high quality of consumable water [2].

Typically, water is disinfected in two stages: primary and secondary. During primary disinfection, chlorine and its derivatives are added to the water and mixed in the water treatment facility. Chlorine gas, sodium hypochlorite, and calcium hypochlorite are some of the chlorine disinfectants used in water treatment facilities [3]. When they are added and dissolved in the water, they react with the water in a process known as oxidation. Oxidation lethally disrupts the cell membranes of bacteria and other microorganisms [4]. As a whole, chlorination effectively eradicates many disease-causing pathogens such as salmonella, Campylobacter, and norovirus [5]. However, a secondary disinfectant stage is necessary because additional microorganisms may be present in outgoing pipes. According to the CDC, waterborne germs can live together in a biofilm—a slimy, glue-like substance that sticks to surfaces such as pipes [6]. In addition to being present in the water as it arrives to the facility, Legionella bacteria can also grow in the pipes leading up your home [7]. Humans can develop pneumonia from inhaling moisture contaminated with Legionella bacteria (e.g., taking a hot shower) [7]. To prevent the contamination and outbreak of this bacteria, ammonia is added to the solution to react with residual chlorine from the primary disinfectant stage to create chloramines. Chloramines are slower to oxidate, which allows them to last longer than primary disinfectants and continue to kill pathogens even after the water leaves the treatment facility [5]. Typically, the outgoing pipes will head to a water storage facility, such as a water tower, or directly to your home faucets.

While the two-stage disinfectant process is very effective at purifying and keeping water safe for consumption, the Environmental Protection Agency promotes constant vigilance by mandating annual Consumer Confidence Reports (CCRs). These reports measure the water’s quality and any presence of other potentially harmful substances such as chlorine-resistant microorganisms and chemical byproducts using mandatory reporting levels. Cryptosporidium is a parasite that enters the water through fecal matter as an oocyst [8]. An oocyst, one of the forms that the parasite takes on during development, has thick walls that better protect the parasite’s inner organelles, making them resistant to many types of chlorine treatments [9].

—continued in Part 2—

References:

[1] Yun Tan, Zahi. “How Do We Get Our Drinking Water in the U.S.?” NPR: National Public Radio, NPR, 2016. https://www.npr.org/2016/04/14/473806134/how-do-we-get-our-drinking-water-in-the-u-s/. Accessed 12 Jul. 2022.

[2] National Research Council (US) Safe Drinking Water Committee. (1980). Chlorines and Chloramines. Drinking Water and Health, Volume 2. 2: 17-23

[3] Adams, Bruce, et. al. “Wastewater Technology Fact Sheet Chlorine Disinfection.” United States Environmental Protection Agency, Office of Water Washington, D.C., 1999. https://www3.epa.gov/npdes/pubs/chlo.pdf. Accessed 14 Jul. 2022.

[4] “6.15C: Types of Disinfectants” Biology LibreTexts, Department of Education Open Textbook Pilot Project, 2021. https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/6%3A_Culturing_Microorganisms/6._15%3A_Chemical_Antimicrobial_Control/6.15C%3A_Types_of_Disinfectants?no-cache. Accessed 23 Jul. 2022.

[5] “Disinfection with Chlorine and Chloramine.” Centers for Disease Control and Prevention (CDC), U.S. Department of Health & Human Services, 2020. https://www.cdc.gov/healthywater/drinking/public/water_disinfection.html. Accessed 5 Jul. 2022.

[6] “Preventing Waterborne Germs at Home.” Centers for Disease Control and Prevention (CDC), U.S. Department of Health & Human Services, 2022. https://www.cdc.gov/healthywater/drinking/preventing-waterborne-germs-at-home.html#anchor_1605186073045. Accessed 5 Jul. 2022.

[7] “Legionella (Legionnaires’ Disease and Pontiac Fever): Causes, How it Spreads, & People at Increased Risk.” Centers for Disease Control and Prevention (CDC), U.S. Department of Health & Human Services, 2021. https://www.cdc.gov/legionella/about/causes-transmission.html. Accessed 14 Jul. 2022.

[8] Ryan, U., Fayer, R. Xiao, L. (2014). Cryptosporidium species in humans and animals: current understanding and research needs. Parasitology. 14: 1667-1685.

[9] Dixon, B.R., (2014). Protozoa: Cryptosporidium spp. Encyclopedia of Food Safety, Academic Press. 2:18-22.

[10] “Disinfection By-Products.” Centers for Disease Control and Prevention (CDC), U.S. Department of Health and Human Services, 2022. https://www.cdc.gov/healthywater/global/household-water-treatment/chlorination-byproducts.html. Accessed 5 Jul. 2022.