Water is integral to life, but much of the water you find in nature is not safe to drink. Sediment, biological contaminants, toxic minerals and even chemical runoff can contaminate water sources and cause illness or even death. Purifying water and making it safe to drink is a multi-step process, whether it is performed by a municipal water treatment plant or a family drawing water from a well.
Sedimentation
The first step in the water purification process is sedimentation. If a volume of water stands for a long time, large particles will eventually fall out of solution, moving to the bottom of the reservoir and leaving clearer water up top. Water treatment plants use a chemical called a flocculant to speed up this process, drawing sediment particles together and increasing their weight so they fall to the bottom more quickly.
Filtration
Once large particles fall out of the solution, the next step is filtration. A filter is any media designed to trap microscopic particles that survived the sedimentation process. Sand and gravel are common filtration media, and many municipal systems use these as a primary filter. The most common type of filter, and one of the most effective, is activated charcoal.
Activated Charcoal
Activated charcoal is a type of charcoal with an extremely large surface area in comparison to particle size. A single gram of activated charcoal may have a surface area of 1,500 sq. m. Activated charcoal attracts organic compounds out of the water that can alter its taste and odor, as well as some types of chemical contaminants. Most home water filters on the market include activated charcoal in their filtration media.
Municipal Disinfection
Biological contaminants are small enough to pass through most filters, so water treatment plants disinfect the water after filtration. The most common method of disinfection is through the addition of chlorine, which kills microorganisms at the expense of adding a distinctive taste and odor to the water. Ultraviolet disinfection is a technique that leaves no residue and sterilizes any bacteria present in the water, preventing them from multiplying. Water treatment plants can also use ozone to destroy living things in the water, although the byproducts of ozone disinfection can cause illness unless filtered out before consumption.
Home Treatment
The most common method of home disinfection is boiling. Bringing a volume of water to 212 degrees F for one full minute will kill any microorganisms. According to the EPA, adding eight drops of chlorine bleach to a gallon of water and letting it sit for 30 minutes will also kill bacteria and viruses present, rendering the water safe to drink.
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