Treatment with Chlorine based compounds and/or Chloramine (NH2Cl)
Chlorine was first used as a drinking water disinfectant in Europe in the late 1800s. New Jersey City, New Jersey began employing chlorine in water sanitation in 1908 1. As for chloramine, it has been used as a drinking water disinfectant in the U.S. in places like Springfield, Illinois, and Lansing, Michigan since 1929 2. Today, chlorine and chloramine are the major disinfectants used to disinfect public water systems.
Chlorination is the process of adding chlorine compounds to drinking water to disinfect it and kill germs. This method is quite cheap for most countries and rids water of bacteria and most viruses. Regarding parasites, results can vary depending upon the type of chlorine product that it used (refer to this CDC table). Chlorine does offer residual protection from treatment facility to consumer.
Different processes can be used to achieve safe levels of chlorine in drinking water. Chlorine is available as compressed elemental gas (Cl2), sodium hypochlorite (NaClO) solution or solid calcium hypochlorite Ca(OCl)2 1. While the chemicals could be harmful in high doses, only small amounts are required for effective chemical disinfection of drinking water 2.
Chlorine dioxide disinfection (ClO2)
This is a faster-acting disinfectant than previously mentioned chlorine sources (referred to as free chlorine). It is relatively rarely used because in some circumstances it may create excessive amounts of , which is a by-product regulated to low allowable levels in the United States. Chlorine dioxide can be supplied as an aqueous solution and added to water to avoid gas handling problems; chlorine dioxide gas accumulations may spontaneously detonate.
Image of chlorine dioxide dissolved in water.
Chloramination is sometimes used as an alternative to chlorination. Chloroamines are a group of chemical compounds that contain chlorine and ammonia (NH3). The specific form of chloroamine used in drinking water disinfection is called monochloramine.
Chloroamines can be produced in swimming pools when bodily fluids (perspiration, mucous, urine, or mucous) react with a chlorine based sanitizer. The resulting products of these reactions are dichloramine and trichloramine The chemicals are sometimes found in indoor swimming pools, can can cause skin, eye, and respiratory problems 3.
Chlorination does alter smell and taste of drinking water. In addition, chlorine can react with other chemicals in tap water to produce organochlorides. The EPA classifies these newly formed compounds as disinfectant byproducts and regulates them as primary drinking water contaminants.
Ozone (O3) Disinfection
Ozone disinfection, or ozonation, is powerful oxidizing agent which is toxic to most waterborne organisms. This method of disinfection is widely used in Europe. Ozone deactivates cyst formation of protozoa (like giardia). In addition, this chemical effectively kills viruses and bacteria.
Ozone machines were first constructed in the mid-1800's. New devices produce O3 molecules by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on-site and then added to the water by bubble contact. Unlike chlorine, the ozonation process does not alter the taste or smell of water.
Unfortunately, ozone does not provide any residual protection once water has been treated. After leaving a water treatment facility, ozone cannot protect the water from new pathogens. For water that must travel far distances to consumers, chlorine or chloramine should be added throughout a distribution system to remove any potential pathogens during the transportation process
However, although fewer by-products are formed by ozonation, it has been discovered that ozone reacts with bromide ions in water to produce concentrations of the suspected carcinogen . Bromide can be found in fresh water supplies in sufficient concentrations to produce (after ozonation) more than 10 parts per billion (ppb) of bromate — the maximum contaminant level established by the EPA. Ozone disinfection is also energy intensive and more expensive than chlorination.
Ultraviolet Disinfection (UV)
Ultraviolet radiation (namely UVC) can be used to eradicate viruses, bacteria, and parasites from drinking water. This method of sanitation does not produce byproducts or alter physical properties (taste or smell) of the water.
However, ionizing radiation has difficulty inactivating parasitic cysts in turbid (unclear) water. Like ozonation, UV irradiation offers no residual protection and is pricier than chlorination. Smaller ultraviolet units do supply over 2 million people in 28 developing countries clean water for drinking, eating, and cooking.
Ultraviolet lamp sanitizing water. Image courtesy of: https://www.nab.usace.army.mil/Media/News-Stories/Article/946068/army-water-treatment-plant-brings-a-unique-first/
Take from 14.6 Making Water Fit To Drink (Delmar)