All of these types of waters can also be polluted, though any bottled carbonated water would be free of microorganisms, as they cannot live there. Generally though, they should be checked out for mineral levels and chemicals if you consume them in any quantity. I do not recommend, however, large amounts of these carbonated waters. The carbon dioxide can get into the blood and affect the acid-alkaline balance, although the body usually handles this easily through respiration or kidney filtration.

Filtered Water
Filtration, or purification, involves the removal of extraneous matter, be it chemicals, metals, or bacteria, from water. Legally, anything called a "purifier" must remove 99.75 percent of incoming bacteria. Americans are purchasing about two million home filtering systems yearly, and there are a great many models from which to choose. There are several types of filtration systems that can be used, including carbon filters, both granulated and solid, and reverse osmosis. (Distillation will be discussed separately, next.) It is a good idea to educate yourself about water filtration before purchasing a home unit. In the long run, home filters/purifiers are the least expensive and safest way to obtain good drinking water.

Activated Carbon (AC) is the most common type of filter. The carbon, used for centuries as a filtering substance, is "activated" by exposing it to chemicals at high temperatures and steam in the absence of oxygen. That gives the carbon a large surface on which to attach and absorb contaminants. Most carbon filtration units mechanically and biomagnetically (ionically) filter the water and remove the unpleasant appearance, odor, and taste by cleaning it of bacteria, parasites, most viruses, chlorine, and the heavier minerals and particulate matter. However, carbon is best at removing organic chemicals and chlorine, not perfect for all microorganisms and metals. Basically, they will filter out any particles or organisms over 0.04 microns, or whatever the size of the filter pores. The filters can, however, collect bacteria and sediment; as a result, there is some concern that they may breed bacteria and dump them back into the water. Hot water should not be run through carbon filters because it can cause contaminant release. Carbon is excellent at trapping the larger molecules, chemicals, and larger microorganisms; it is not good at removing inorganic minerals including fluoride bound strongly to sodium or calcium, the way it is added to municipal waters. However, solid carbon filtration is believed to be relatively effective (this is still controversial) at removing many of the toxic minerals with higher molecular weights, such as lead or mercury.

The two main types of carbon filters are granulated carbon and solid carbon block filters. The granulated carbon filter has air spaces between the carbon particles to trap bacteria and remove it from the water; however, the bacteria can multiply within the air spaces. Silver is used in most granulated filters to assist in killing the bacteria. These "silver-impregnated" filters do help reduce the bacterial growth within the filter, but there are concerns about ineffectiveness and silver toxicity. Though granulated carbon filters are economical, their use is short-lived, and their safety is definitely questionable; I do not recommend them.

The Solid Carbon Block with its surrounding filter alleviates the concern of microorganism contamination. Not only can the filtering surface area of this denser carbon bed clean much more water but, because there is very little oxygen or supply nutrients within the filter, the germs will not thrive; however, to be safe, if the filter is not used for a day or longer, let the water run through it for 10–20 seconds before drinking. Research has demonstrated that these units also trap more chemicals, organic pollutants, radon, and asbestos than the looser granulated carbon filters. Some companies that sell solid carbon block water filters are Multi-Pure, NeoLife, and Amway.