Different Ways to Purify Water

Water that is biologically contaminated or toxic must be purified before it is suitable for drinking and other purposes. Biologically contaminated water contains bacteria, and sometimes viruses and protozoa, that may cause gastrointestinal issues or other illness if consumed. Toxic water may also contain chemicals, such as pesticides, which are toxic to humans and many other animals. Water can undergo one or many purification processes, depending on the purpose for which it will be used.

Natural

• Water is naturally filtered through soil, rocks and plants. When it rains, the ground absorbs the water. Groundwater emerges many years after the rainfall that created it, with harmful debris and bacteria often removed by the rocks and soil that surround it. Harmful bacteria may still remain in groundwater, however. It is impossible to tell by sight what exactly the water has flowed through and where it came from.

pH

• Drinking water should ideally have a pH of 7, a neutral point that is neither alkaline (basic) nor acidic. When the pH of water is lower than 7, the water is acidic. Chemicals such as lime are then added to raise the pH and make it alkaline. Acidic water is dangerous because as it flows through copper or lead pipe systems, it may dissolve and contract these chemicals, which are toxic for human consumption.

Flocculation

• Flocculation is a process that makes water clear. Coagulants such as aluminum hydroxide and the homopolymer polyDADMAC are useful for flocculating water. After adding these agents, water treatment facilities stir the water until particulate matter begins to stick together and becomes suspended. Once the matter is suspended, it's easy to remove.

Sedimentation

• After flocculation, the water must be filtered through at least two more methods, including sedimentation and filtration. In a sedimentation tank, floc falls to the bottom due to the slow flow of the water. The longer the water is in the sedimentation tank and the deeper the tank is, the more floc will fall and be removed. The fallen floc becomes a layer of sludge on the bottom of the basin and must be cleaned regularly.

Disinfection

• Disinfection involves the use of chemicals such as chlorine for purification. Chlorine kills pathogens that have survived the previous steps of filtration; E. coli may be one of them. Most public water systems require chemical disinfection.

Boiling

• Rick Curtis, author of "The Backpacker's Field Manual," notes that boiling water is the most certain way to kill harmful pathogens. "According to the Wilderness Medical Society, water temperatures above 160 degrees Fahrenheit (70 degrees Celsius) kill all pathogens within 30 minutes, and above 185 degrees Fahrenheit (85 degrees Celsius) within a few minutes," he writes. If you let your water boil rapidly for just a few minutes, all microorganisms present should be dead.