Carbon water filtration is a water filtration technique which relies on passing water through a carbon filter to remove some impurities. Carbon filtration is one of the oldest water filtration techniques known to human society, with numerous ancient cultures using some variation on the carbon filter to make their water cleaner and fresher-tasting. Numerous styles of carbon water filtration systems are available, ranging from pitchers used to filter drinking water to whole house filtration systems which scrub all of the water which enters a house.
Block carbon and activated carbon are both used in water filtration. In either case, the carbon is extremely porous, with a large surface area. As water moves through the carbon, materials like sediment, volatile organic compounds, and chlorine are attracted to the carbon, sticking to it in a process called adsorption. Eventually, a thin film coats the carbon and it is no longer effective, causing water to move sluggishly and leaving impurities in the water. At this point, the filter must be changed.
Carbon water filtration will not trap every impurity in the water. Inorganic compounds and bacteria are generally not trapped by such filters, for example. In fact, a carbon filter can actually create a breeding ground for bacteria, which is one reason why these filters need to be replaced in a timely fashion. Water with impurities like arsenic and nitrates requires other types of filtration to remove these impurities. For this reason, water testing is sometimes recommended before adopting a carbon water filtration system, to confirm that the system will be effective.
People often use carbon water filtration to improve the taste and appearance of water. Bad odors and unpleasant flavors are removed, along with some sediments which discolor water and make it unappealing to look at. More extensive water treatment to remove bacteria and viruses will be necessary if water is known to contain these impurities. Since carbon water filtration is often used on municipal water which has already been treated, disease-causing organisms are not a major concern.
Some people prefer the taste of water which has been subjected to carbon water filtration. It tends to have a crisper, cleaner flavor as a result of the removal of some impurities. Filtered water may also be recommended for certain applications; for example, high chlorine contents in plain tap water might be dangerous for sensitive fish, requiring aquarists to filter their water with a carbon filter to keep their fish healthy and happy.