The Blue Planet – certainly an appropriate nickname for Earth, where around 71% of the surface is covered in water. Maybe more importantly to us as humans, though, is that a small fraction of this water is freshwater... less than 3% of the water on Earth. And only a small fraction of this freshwater is accessible for drinking. Drinking water is an extraordinarily precious resource, and access to clean drinking water is an even greater privilege. This week, we’ll take a look at what actually causes drinking water contamination as well as drinking water treatment technologies used around the world. Pour yourself a glass of H2O and let’s dive in...
why treat water?
Seeing a container of muddy water may not look totally appetizing, but it’s often the contaminants we can’t see that pose the most danger. Physical contaminants, like soil and trash, are only the tip of the iceberg. Here we’ll cover some common biological and chemical contaminants along with a few contaminants that are a bit less understood.
Biological contaminants are a particularly nasty bunch that have caused widespread outbreaks of water-borne disease throughout human history. Giardia, Salmonella, Cryptosporidium, Legionella, Cholera, Rotavirus and even certain toxic algae are just a few microorganisms that can infect humans through drinking water. Many of these water-borne microbes spread when human feces infects the drinking water source.
Typhoid fever is caused by a strain of Salmonella bacteria that can be transmitted through drinking water. Though the United States doesn’t face as many water-borne disease outbreaks today, this was not the case prior to chlorination of drinking water.
Cholera has been a major source of water-borne disease in both the past and present. One notable cholera outbreak occurred in London in 1854 when John Snow, considered the “father of modern epidemiology”, postulated that the outbreak was caused by drinking water from a local water well. At this time in history, people weren’t aware that the disease was spread via water. John Snow had the handle of the water well removed, and the cases of cholera in the area grinded to a halt. Pretty impressive for 1854, but cholera is still very much an issue today. After the earthquake in Haiti in 2010, a breakdown in sanitation systems caused a severe outbreak of cholera which caused well over 8,000 deaths. The United States may have high water quality standards, but the country is not immune to waterborne diseases either. According to Centers for Disease Control (CDC) data from 2013-2014, multiple outbreaks occurred in the United States during the two-year period causing over 500 cases and 13 deaths from Legionella bacteria alone.
Chemical contaminants constitute a wide category and can include heavy metals, pesticides, petroleum compounds, fertilizers, solvents, hormone disruptors, and even chemicals that are created as a by-product of water treatment itself. Some of these chemicals, such as the heavy metal arsenic, can simply be naturally occurring and just need to be monitored to avoid levels that become dangerous to humans. A vast number of the chemicals that can contaminate drinking water, though, are man-made.
Water runoff and spills from mining operations has caused heavy metal contamination in surface waters and groundwater, such as the 2015 Gold King Mine Spill in Colorado. Most people are no stranger to oil spill incidents, either, such as the BP Deepwater Horizon oil spill in 2010. Outside of spills and accidents, modern-day farming operations can also cause chemical contamination of drinking water. Applying too much fertilizer can cause excess nitrate chemicals to be washed away with rain into rivers and other surface waters. The City of Des Moines, Iowa actually filed a lawsuit in 2015 to regulate farmers’ fertilizer application in the area due to elevated and dangerous levels of nitrate found in drinking water sources for the city. Water distribution systems themselves can also create chemical contaminants. Drinking water contamination occurred in Flint, Michigan (Flint Water Crisis) when corroded drinking water piping leached Lead metal into the water system.
A picture showing a river affected by the 2015 Gold King Mine spill in Colorado.
Other contaminants coming from man-made chemicals might not be as well understood, but still certainly raise concerns. These chemical contaminants include pharmaceuticals, microplastics, and a class of compounds called PFAS (PerFluorinated Alkyl Substances) among others. Pharmaceuticals in drinking water are a somewhat pervasive since both sewage treatment plants and drinking water treatment plants aren’t built to remove pharmaceuticals from water, and they aren’t necessarily explicitly tested for in most instances. These pharmaceuticals include products such as antidepressants, blood thinners, heart medications, hormones, painkillers, and carbamazepine (an antiseizure drug) among many others that have been found in surface waters throughout the United States. Just due to normal water treatment operation, a large percentage of these pharmaceuticals do get removed from water before we drink it fortunately, but trace amounts still get through. Pharmaceuticals found in surface water actually come from a number of sources:
Discarded medication from nursing homes, hospitals, and people’s own houses
Releases from pharmaceutical manufacturers
Runoff from livestock operations where animal waste contains residual hormones and antibiotics
Waste from humans, since our bodies don’t always entirely use up medication
The level of pharmaceuticals that we end up drinking are very low, and any effect on humans has not been proven or widely accepted. For wildlife, though, the effects of these pharmaceuticals have become more apparent, especially fish. Scientists have found popular antidepressant medications concentrated in the brain tissue of fish downstream from wastewater treatment plants. Some studies also found that the populations of female and intersex fish are higher in highly polluted areas, likely due to elevated estrogen levels in the water from hormone-based medications.
PFAS are another class of chemicals that have become a greater concern as more and more studies show that they are nearly ubiquitous and persist in the environment without breaking down. In fact, CDC studies show that the blood of nearly every single American contains PFAS. These compounds were used to make compounds such as Teflon (used on non-stick cookware). Check out this interactive map from the Environmental Working Group (EWG) to see PFAS test results from water around the United States: https://www.ewg.org/interactive-maps/pfas_contamination/map/
A screenshot from EWG’s interactive PFAS mapping tool.
Drinking water treatment
Thankfully, a number of different technologies have been developed to treat water for most contaminants so that it’s safer to drink (sorry, cholera, nobody really liked you anyways). Drinking water comes from a variety of sources including groundwater, lakes, ponds, rivers, rainfall, and even the ocean. Due to the variety of drinking water sources that have different amounts of contaminants, treatment technologies are usually tailored to fit local needs and resources. Most of these technologies are combined with one or two others in order to address different contaminants. A few of the main technologies used to treat water are outlined below...
Filtration: This is probably the most apparent type of treatment method; basically, the water flows through tiny holes that contaminants can’t fit through. Since water molecules are extremely small (less than a nanometer) compared to most physical and biological contaminants, this method is actually pretty effective. Using the correct filter, though, is key to success. The type of filtration could range in size from gravel, which only removes larger contaminants, all the way down to nano-filtration membranes, which can even remove viruses. While smaller filters sound great, more energy is typically required to push the water through the filter as the filter size gets smaller.
Filter sizes available for water treatment
Reverse osmosis: Reverse osmosis could almost be considered a special type of filtration, but this treatment technology is being addressed separately because of its use in desalination of ocean water. Since reverse osmosis can be used to remove chemicals as tiny as sodium ions, it is able to remove most salt from ocean water, making it possible to drink.
Biological filtration: Also a special type of filtration, biological filtration uses the power of microorganisms to eat up contaminants in the water. Some microorganisms will even remove contaminants such as residual pharmaceuticals. The filter itself provides a nice home for the microorganisms to live in as they’re put to work.
Diagram showing how “floc” solids settle to the bottom while the treated water (clarified effluent) is collected at the top
Coagulation and flocculation: Coagulation and flocculation involve the addition of chemicals to improve water clarity and remove some biological contaminants. When paired with other treatment technologies, coagulation and flocculation is typically one of the first treatments applied to the water. Chemicals such as aluminum sulfate and certain polymers are added for this process, and they function by essentially “collecting” suspended particles until they form larger particles that settle out to the bottom. The larger particles that form and settle out are called “floc”. Water remaining at the top, above the floc, is collected for drinking water or further treatment.
Chlorination: Water chlorination is a form of chemical treatment in which chloramine, hypochlorite, or simply chlorine gas is added to water in order to kill biological contaminants that cause disease. This method of water treatment is popular in the United States. Low levels of these chlorinated compounds are not harmful to humans, although they can sometimes add unpleasant flavor or odor to the water. Water chlorination typically occurs in most systems just prior to distribution since residual chlorine helps kill off any biological contaminants that enter the water as it travels through pipes or distribution lines. Swimming pools that use chlorination to kill germs make use of different chlorine-based chemicals, such as trichloramine.
Ozone: Commonly used in European countries as part of the water treatment process, ozone treatment is a form of chemical disinfection. Ozone is a gas which kills biological contaminants and can also help break down some chemical contaminants due to its high reactivity. Since ozone is so reactive, it works very quickly and returns to its oxygen form, minimizing any effect on odor or taste. The quick reaction, though, makes it less suitable for maintaining clean water as it runs through pipes (unlike chlorine).
Distillation: Boil water, collect the steam, and cool the steam until it becomes purified liquid water again. Pretty straightforward. Around 70% of the desalination plants in the world are located in the Middle East where oil-rich countries with few sources of freshwater will distill ocean water in order to remove salt and other contaminants. While distillation is effective for removing contaminants, it is highly energy-intensive.
A woman laying out clear bottles of water for solar disinfection.
Ultraviolet (UV) Radiation: A bit stronger than the UV light that causes sunburn and skin cancer, the UV radiation used in water treatment can destroy bacteria, viruses, parasites, and even some chemical contaminants such as pesticides. The UV radiation is generated by high-energy lamps that never even touch the water. Similar to ozone treatment, UV radiation destroys contaminants quickly but does not maintain clean water as it runs through the pipes or distribution system. It’s also important to note that a low-tech version of UV radiation could be considered “solar disinfection” which is sometimes used in areas without well-developed treatment systems. In solar disinfection, water-filled containers are left out in the sun for extended periods of time so that the combination of heat and UV radiation from the sun (a weaker form of UV radiation) kill a large portion of biological contaminants.
There are certainly more water treatment methods out there, such as activated carbon filtration, so feel free to explore other alternatives! These same methods are also employed on a smaller scale in home water treatment devices, such as Brita filters.
water for everyone?
Percent of schools with basic drinking water services by country.
Water treatment has come a long way in recent history, but many throughout the world still do not have access to clean water. Data presented by UNICEF and the World Health Organization show that 100% of schools in the United States have basic drinking water services, which is significant compared to the country of Guinea where only 9% of schools have basic drinking water services available.
The World Health Organization also estimated that in 2017 close to 579 million people around the world obtained drinking water from unprotected wells/springs or from untreated surface waters such as lakes. Even the United States is not immune to drinking water issues, as seen in the Flint, Michigan water crisis that began in 2014. Managing where we get water, how we treat it, and how we distribute it are key to maintaining a safe and accessible supply for everyone. Just as important, though, is keeping track of what we release into water that can come back to bite us later (e.g. pesticides or toxic metals).
In the end, we all need water to live. One poet, W.H. Auden, is even quoted with writing: “thousands have lived without love, not one without water.” Maybe not the the most upbeat thing to write, Mr. Auden, but I’ll drink to that (water, of course).
To Think About...
Where does your drinking water come from (e.g. a groundwater well or a nearby river)?
What might be the biggest sources of water contamination in your area?
If your current water supply became contaminated, what would you use as an alternative?
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