In its passage from the clouds to the tap, water comes in contact with many different substances, including gases, minerals, and organic matter, which are carried either as solid particles or are completely dissolved in water.
A wide variety of filters are available to remove the numerous different contaminants found in water. The specific type of filter required in the home depends, of course, on the kinds of impurities in the water and the amounts present. Basically, filters provide a screening which traps the contaminants in the water as it flows through the filter. If the contaminated particles are large enough, the filter simply traps them. In other cases, a chemical reaction may first be necessary to make the particles of sufficient size to permit their collection on the filter media.
IRON FILTERS (OXIDIZING FILTERS)
Iron/oxidizing filters are used for treatment of waters with medium concentrations of iron, manganese, or hydrogen sulfide. Iron appears in water in both a ferric (visible and insoluble) and a ferrous (dissolved) state. While ferric iron can be simply filtered from the water, ferrous iron must be oxidized, converting it to the suspended ferric state, in order to be filtered out. The media used in these iron filters is manganese green sand, which is capable of oxidizing dissolved iron and manganese, allowing them to be filtered out in the same tank.
Iron/oxidizing filters must be periodically backwashed, to flush away accumulated deposits, then regenerated with a potassium permanganate solution. After rinsing, the filter is again ready for operation. When such filters are used, they are, in most cases, placed ahead of a softener.
The sand filter is used for the simple filtration from water of visible dirt or suspended matter (turbidity) due to silt, sand, organic matter, and rust type particles. These units use sand or gravel as the filter media, and are effective in removing sediment and cloudiness from water, except when such turbidity is due to extremely fine particles. Sand filters must be backwashed periodically to clean the suspended matter from the filter media and flush it down the drain.
ACTIVATED CARBON FILTERS
Activated carbon filters are primarily used to remove objectionable tastes and odors from water, and are effective in removing chlorine. These filters contain activated carbon, a form of charcoal with high adsorptive qualities. Adsorption is defined as the adhesion of a gas, vapor, or dissolved material on the surface of a solid. As water is brought into contact with these activated carbon particles, the taste and odor constituents are retained in the carbon, resulting in a taste and odor free water. Activated carbon filters have also proven effective in the removal of inorganics such as trihalomethanes. The granulated filters must be periodically backwashed, and the cartridges cleaned or replaced from time to time.
To increase the pH value of a water, which is to decrease the acidity and thus its corrosive nature, a neutralizing filter is recommended. The presence of large amounts of free carbon dioxide gas in solution (carbonic acid) renders a water acid in character, which can cause corrosion damage to the metal components of a water system, including the water pump, piping (iron, galvanized brass, and even copper), tank, water heater, and fixtures. Neutralizing filters contain a bed of materials such as calcite and magnesia. As water passes through this bed, the carbonic acid is neutralized and a small amount of the bed is dissolved. As a result, the water becomes more alkaline (higher pH value) and thus less corrosive. A neutralizer requires occasional backwashing to loosen the material and clean the bed. From time to time, additional material must be added to the bed to replace that which is dissolved.
CHEMICAL FEED PUMPS
Chemical feed pumps are used to inject corrective solutions into a water supply. For example, soda ash, a highly alkaline compound, is often added in solution to a water supply as an alternate method for reducing acidity. Chemical feed pumps can be wired to operate in conjunction with an electrically operated well or water pump, and multiple solutions can be fed into a water system with a single pump unit when applicable. Chemical feed storage tanks are occasionally an attractive solution to water treatment problems because several chemicals can be mixed and fed together, thus solving several problems at once (e.g. chlorine for purification and acid neutralizer for pH control). Chemical feed storage tanks must be refilled with the chemical compound periodically.