Water treatment and infectious diseases
Water treatment is the process of purifying water to remove contaminants, making it safe for various uses, including drinking, cooking, and bathing. Effective water treatment is crucial for preventing waterborne infectious diseases caused by pathogens like Cryptosporidium, E. coli, hepatitis A, and Giardia, which can lead to severe health issues, including dehydration from diarrhea. The treatment process typically involves several steps: coagulation, where larger solids are removed; sedimentation, which allows smaller particles to settle; filtration, which clears remaining impurities; and disinfection, primarily through chlorination, to eliminate pathogens.
Clean water should be clear, colorless, odorless, and free from harmful materials. While surface water generally requires more extensive treatment due to higher levels of pollutants compared to groundwater, both sources undergo similar purification processes. The Safe Drinking Water Act in the U.S. sets standards for drinking water quality, yet emerging contaminants like pharmaceuticals pose new challenges for water treatment facilities. In regions lacking robust water treatment infrastructure, point-of-use devices have become vital in improving water safety. Despite advancements, issues remain; unsafe drinking water continues to be a leading cause of illness, underscoring the importance of effective water treatment in public health.
Water treatment and infectious diseases
- ALSO KNOWN AS: Water purification
Definition
Water treatment is the process of removing contaminants from water to make it safe for drinking, cooking, bathing, and swimming. Without water treatment, waterborne pathogens such as Cryptosporidium species, Escherichia coli, hepatitis A virus, and Giardia intestinalis (also known as G. lamblia) can proliferate and cause illness and death, often from the dehydration that follows diarrhea.
Clean water is expected to be clear, colorless, odorless, and tasteless. This requires that water be free of particulates (minute substances). Treating water involves the killing of microbes such as bacteria, viruses, and parasites, and the binding and removal of minerals such as iron, calcium, magnesium, manganese, and sulphur.
To clean water, a series of specific processes must be performed: physical separation of solids by settling and filtration; chemical reactions of coagulation and disinfection; and biological methods such as aeration, bacterial digestion of sludge, and filtration through natural materials. The choice of processes depends on the nature and volume of the water to be purified. An analytical survey must be performed initially.
Two original sources of water exist: surface water and groundwater. Surface water comprises rivers, lakes, streams, and ponds. Groundwater is accessible by digging wells. Groundwater generally requires less water treatment than surface water, which contains more debris and pollutants.
Treatment Processes
Coagulation. When water is first received at a water-treatment plant, large pieces of solid material, such as sewage, are removed by a coarse screen and then discarded. Smaller solid particles are then induced to bind together so that they will form into larger particles through coagulation. Ions with multiple charges (polyelectrolytes) change the pH (acidity) of the water and trigger chemical reactions that cause aggregation. Alum is frequently added to attract dirt particles, which may contain herbicides and pesticides. Lime and soda ash cause calcium and magnesium to precipitate, thus softening the water.
Sedimentation. The material resulting from coagulation, called floc, has sufficient weight that it sinks to the bottom of settling tanks. This separation of solids by sedimentation is time-consuming. Algae eventually rise to the surface, where they may be skimmed. The clearer water on the surface is then slowly siphoned for filtration. Aerobic and anaerobic bacteria may be added to the withheld solids (sludge) to digest organic waste matter and neutralize pollutants. Carbon dioxide, ammonia, and methane gases are generated. The digested sludge may then be used as a fertilizer supplement in farming.
Filtration. Any remaining particles in the water may be removed by filters made of artificial membranes, nets, or natural materials. Water may be filtered by passing it through beds of sand, gravel, or pulverized coal. Activated charcoal may be added to the water first to remove color, odor, taste, and radioactivity. In another method of removing calcium and magnesium, water may be passed through ion exchange columns, in which sodium ions compete with these cations for binding to porous material.
Aeration is used to remove dissolved elements such as iron, sulphur, and manganese. Air is forced into the water to remove carbon dioxide, hydrogen sulfide, and other gases. In diffused aeration, air is bubbled through the water. In spray aeration, water is sprayed through the air.
The process of removing salt from the water, called desalination, is often used to make ocean water drinkable in places where fresh water is scarce. The salt is removed by microfiltration and by reverse osmosis.
Disinfection. Disinfection is the general method of killing pathogens (bacteria, viruses, and parasites). The most common method of water disinfection is chlorination with sodium hypochlorite bleach. Used less frequently are ultraviolet light and ozone aeration. Home water filtration systems that use ultraviolet light to further disinfect water after filtering are more effective than those without this feature. (To disinfect water in one’s home in an emergency, one should boil the water to kill microbes.)
Storage
Treated water must then be stored and delivered under clean conditions to prevent recontamination. The water is stored in closed tanks or reservoirs; from there, it is piped to homes, businesses, and other facilities. Minimal chlorine may be added at this stage to maintain cleanliness. Fluoride also may be added to the treated water as a method to prevent tooth decay.
Impact
The U.S. Safe Drinking Water Act of 1974 established national drinking-water standards, which includes maximum acceptable contaminant levels. The act was amended in 1986 and 1996 to protect natural water sources. The original act was intended to address drinking water as it flowed into homes, businesses, and public drinking fountains. The amendments address water safety as it flows from the original water source to the faucet.
Most water-treatment plants were not designed with the capability to remove pharmaceuticals, including natural and synthetic hormones, that are flushed down the sink or toilet. As a result, prescription medications have been identified as an emerging contaminant in the twenty-first century. In response, certain treatment plants use the chemical oxidative processes to remove estrogen and other medications from the water supply, but the process generates disinfection byproducts in the water supply that pose potential risks to human health. A 2019 study published in Chemical Reviews examined infrastructure upgrades that were undertaken in water treatment plants in order to counteract the increased prevalence of pharmaceuticals in the water supply. These technologies include destroying the contaminants using ultraviolet degradation, filtering out the contaminants using reverse osmosis and nanofiltration, and the removal of contaminants through the process of adsorption (using a material that chemically and physically bonds to contaminants). Community-level prevention efforts include the collection of unused and unwanted over-the-counter and prescription medications for disposal by authorized incineration.
In developing countries that do not have access to the necessary water decontamination infrastructure, point of use (POU) devices, water filters that treat water at the point of consumption, have become an effective method in the treatment of drinking water through the removal of pathogens. A 2018 study published in NPJ Clean Water analyzed the implementation of POU devices and concluded that the devices are an important factor in the immediate remediation of health crises that result from the consumption of contaminated water in countries that do not have adequate water treatment infrastructure.
Despite efforts to effectively treat water and prevent illness, Our World in Data estimated that diarrhea caused around 1.6 million deaths each year between 2015 and 2019—unsafe drinking water being among the highest risk factors. In the United States, the Centers for Disease Control and Prevention estimates that 7.15 million illnesses occur annually due to waterborne infections.
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