In the United States, drinking water is governed by Environmental Protection Agency (EPA) guidelines that consider the chemical content, appearance, smell and taste. The primary legislation covering these guidelines is the Safe Drinking Water Act (SDWA) of 1974. The SDWA maintains standards for over 90 different contaminants that may enter drinking water at its source or during processing, specifying a “maximum contaminant level” for each. This level sets a limit on the legal acceptable mount of any contaminant in drinking water in the country. Based on accepted scientific research, these maximum contaminant levels protect users from waterborne chemicals and diseases, and make drinking water in the country safe to drink. The EPA states that the due to the SDWA, 90 percent of all drinking water in the United States meets safety requirements and matches appearance, taste and smell requirements.
If a user wants to ensure their drinking water is compliant with EPA rules, they can contact their water supplier to obtain an annual water quality report, which all water suppliers are required to make available. Often, these reports are posted online for easy access.
However, these rules and checks only ensure water is safe from the supplier source. Sometimes, water can be further contaminated by home pipes, especially if the pipes were installed decades ago when lead was not seen as a danger. Home testing kits are available to examine water contamination and pinpoint needs for further purification.
If a user wishes to further purify water supplied to their house or business, the most effective method is chemical water purification. Although boiling water (distillation) can remove bacteria, and household carbon-based water purifiers can remove certain contaminants, they cannot fully clean unsafe water. In fact, water suppliers use a variety of methods to purify the water they supply to a municipality or other community. As a result, there are a broad range of techniques for purifying water. The following methods are used either in full or in part as components of a complete water purification system.
Flocculation: Flocculation isn’t a purifying method, but rather a clarification process. It is used to make cloudy or turbid water clear. Generally, flocculation is accomplished by adding particulate minerals to the water which soak up or attract particles, and then passing the water through a filtration device to remove these larger mineral particles. The three most regularly-used flocculation agents are iron (III) hydroxide, aluminum hydroxide and PolyDADMAC.
Sedimentation: Sedimentation uses a slow-flow basin: sediment in water settles at the bottom of the container. Next, it is removed and treated. This sediment will often form a layer of sludge at the bottom of the water container, which makes up approximately three to five percent of total water volume.
Filtration: There are a few types of filtration, which is the process of removing unsettled or ungrouped sediment left in the water.
· Sand filters. Either fast or slow, sand filtration passes water through sand that contains activated carbon. Microporous carbon allows small bits of sediment to adhere to the carbon, which is then large enough to be sluiced free from the water.
· Lava filters. Similar to sand filtration, lava filters adhere small pieces of carbon to floating sediment before the carbon itself is later removed.
· Membranous filtration. Some types of filtration use polymer membranes to prevent sediment from passing through with water.
Disinfection: Disinfection involves treating water with chemicals that kill off bacteria, viruses and other microscopic elements. There are a number of chemicals used in disinfection.
· Chlorine. Chlorine is the most commonly-used disinfectant because it is a strong oxidant and kills microbes rapidly. However, chlorine is also toxic, and if it is released, it can cause health issues for the user. It is important to insure natural organic compounds do not come into contact with chlorine because they can form trihalomethanes and haloacetic acids, which are deadly to humans.
· Chlorine dioxide. Chlorine dioxide is more effective than chlorine, but because it is more difficult to prevent unwanted chemical reactions between chlorine dioxide and other chemicals, it is not often used.
· O3. O3 effectively deactivates cyst-causing protozoa, but it can also form bromate, a carcinogen.
· Hydrogen peroxide. Hydrogen peroxide is a very thorough disinfectant agent, but it is slower acting than other options.
· Ultraviolet light. Ultraviolet light can be used to disinfect clear water by destroying cysts in a way that does not leave residues. However, if water is cloudy, the light cannot penetrate the water and properly dispose of infecting agents.