What is water filtration?

Water filters have a long history as a method of water purification, beginning as early as 2000 b.c.e. in ancient Egypt. Filtration has evolved from the simple Hippocratic sleeve of ancient Greece, made from cloth, to the complicated solid block carbon and multimedia water filters currently on the market. Water filtration is now the premier method of water purification, removing more water contaminants, more efficiently, than any other technique.

The Process
The filtration process involves some type of filter media, over which water flows. This filter media blocks passage of contaminants through physical obstruction, chemical adsorption, or a combination of both processes. Material construction of the filter media varies widely, but the most effective medias are made from carbon or a combination of carbon with other elements.

Modern filtration technology allows water filters to remove more and more contaminants through the chemical process of adsorption. In the adsorption process, contaminants are encouraged to break their bond with water molecules and chemically adhere to the filter media. Generally, water goes through several stages of filtration to ensure that each filter media will remove the ultimate number of contaminants.

Water normally passes through a water filter at a relatively low speed, in order to ensure adequate contact time with the filter media. Once the water has passed through the required stages of filtration, it emerges as pure drinking water, free from contamination.

Treatment Techniques and Devices

Once contamination is detected in a drinking water supply it is important to use the proper treatment device to remove the contaminant. The following section is intended as a guide to help in the selection of a treatment device. Before buying a treatment device have the water supply tested for contamination and consult a specialist when selecting the best treatment device. If the specific contaminant is known the information in the following sections will indicate the possible treatment devices and link to more detailed information on this web site.

Activated Alumina is a granulated form of aluminium oxide. In this process, water containing the contaminant is passed through a cartridge or canister of activated alumina. The alumina absorbs the contaminant and freshwater continues to the service faucet. The cartridge of activated alumina has to be replaced periodically. It is important to determine by testing when the contaminant removal capability of the device is exhausted, so the treatment technique will remove, not contribute to, the contaminant. Also, activated alumina devices will accumulate bacteria, so treated water will have higher bacteria counts than raw water.
Contaminants Removed: Arsenic, Fluoride.

Activated carbon filters absorb impurities from water as it passes through a carbon cartridge or tank. Such filters are used to eliminate or remove undesirable odors, tastes, organic compounds, and residual chlorine. Carbon filters also remove some potentially, hazardous contaminants such as radon gas, hydrogen sulfide, many dissolved organic chemicals and trihalomethanes. Most inorganic chemicals are not removed by these filters.
Contaminants Removed: Hydrogen Sulfide, Radon, Chlorine, Volatile Organic Compounds, Pesticides, Benzene, Colors, Odors.
Related Items: Whole House Carbon Filters

Aeration systems spray the water through an air-filled chamber then use a fan to move the contaminated air out of the area.
Contaminants Removed: Hydrogen Sulfide, Radon.

Anion exchange units use a resin that exchanges chloride, or in some cases hydroxide, for the contaminant anions. Most use chloride which increases the chloride content of water as it removes anions such as nitrate, sulfates and bicarbonates.
Contaminants Removed: Nitrate, Sulfate, Fluoride, Tannins.
Related Items: Nitrate Filters, Tannin Filters

In chemical precipitation certain compounds are added to the water that chemically react with the contaminate. The products of the reaction will then either sink to the bottom or float to the top of the holding tank, so that they can be removed. This method is primary used in public water supplies and is not a viable solution for private water supplies. If contaminant is detected in a private water supply use an alternate method or contact you local water authority.
Contaminants Removed: Arsenic, Barium, Cadmium, Chromium, Lead, Mercury, Selenium, Silver.

The most common, oldest and relatively inexpensive method used to disinfect water is chlorination. A chemical feed pump continuously dispenses chlorine into the water supply. Chlorine, an oxidizing agent, kills most bacteria and some viruses. In the proper concentrations and under adequate exposure time, chlorine is an excellent disinfectant.

Chlorine reacts with certain metals and organic matter in the water to form hazardous, chlorinated, organic chemicals. Use of an activated carbon filter after chlorination will remove excess chlorine and limited amounts of any chlorine compounds formed. Chlorination may also oxidize and remove some color and odor causing substances, including iron and hydrogen sulfide.
Contaminants Removed: Bacteria, Iron, Hydrogen Sulfide, Some Viruses.
Related Items: Chlorinators

Distillation heats water until it vaporizes as steam. Minerals, bacteria and other substances are left behind when the steam recondenses into relatively pure water. Distillers remove bacteria, minerals, trace amounts of metals, many volatile organic chemicals and nitrate. The distillation process is very slow (daily capacity is usually between two and five gallons). Approximately five gallons of tap water is required to produce one gallon of distilled water.
Contaminants Removed: Bacteria, Lead, Nitrate, Sodium Chloride, Organic Chemicals, Many Pesticides.
Related Items: Distillers

Ion exchange systems soften hard water by removing the minerals (calcium and magnesium that cause hardness. This system also efficiently removes iron, manganese and many heavy metals. The hard water is pumped through a tank containing an exchange resin. Sodium on the resin replaces the hardness minerals. The sodium remains in a soluble form in the softened water.
Contaminants Removed: Iron, Magnesium, Calcium, Manganese.
Related Items: Water Softeners

Mechanical filters, or microfiltration, removes suspended material from water including sand, silt, clay or organic matter. These filters do not remove dissolved or very fine particles and are often used in combination with other treatment equipment. Filters are commonly of fabric, fiber, ceramic or other screening material.
Contaminants Removed: Sediment
Related Items: Whole House Sediment Filters

Neutralizing filters treat acidic water. The filter treats all of the home water supply by passing it through granular calcite (marble, calcium carbonate or lime) or by chemically feeding in soda ash, sodium carbonate or caustic soda (sodium hydroxide).
Contaminants Removed: Acidity.
Related Items: pH Neutralizing Filters

Oxidizing filters use a zeolite coated filter to oxidize dissolved iron, manganese and hydrogen sulfide. The contaminants then form large particles that the filter can catch.
Contaminants Removed: Hydrogen Sulfide, Iron, Manganese.
Related Items: Manganese Greensand Filters, Birm Filters

Reverse Osmosis (RO) units remove substantial amounts of most inorganic chemicals (such as salts, metals, minerals) most microorganisms, and many organic chemicals. They do not effectively remove some organic compounds. Mechanical filters and activated carbon filters are almost always used with a RO unit. First, the mechanical filter (1) removes dirt, sediment and other impurities, that would otherwise clog the reverse osmosis membrane. The RO (2) unit is installed next. The water is held in a pressurized water storage container (3). An activated carbon filter (4) then removes organic compounds which pass though the RO unit. A separate water tap (5) is used for this water.

Reverse Osmosis uses large amounts of water. Typically, about 75% or more of the water is discarded with the contaminants.
Contaminants Removed: Lead, Sulfate, Calcium, Magnesium, Sodium, Potassium, Manganese, Aluminum, Chloride, Nitrate, Fluoride Boron, Most Microorganisms, Organic Chemicals.
Related Items: Reverse Osmosis Filters

Low-pressure mercury arc lamps produce ultraviolet light which has germicidal properties. The radiation kills or deactivates pathogens. Bacteria are killed with relatively low amounts of radiation, viruses are more resistant, and cysts and worms are unaffected. Radiation leaves no residual product that continues to disinfect beyond the treatment period.
Contaminants Removed: Bacteria, Viruses, Cysts such as Cryptosporidium and Giardia.
Related Items: Ultraviolet Filters

Common Aesthetic Problems and Solutions

Symptom Probable Cause Treatments
Hard water deposits on kettles, pots, hot water heaters, humidifiers Excess calcium Water softener
Reverse Osmosis
Anti-Scale Units
Rusty red or brown staining of fixtures or laundry and/or your water has a metallic taste

Excess iron

Water softener
Whole house iron filter

Black staining of fixtures or laundry

Excess manganese Water softener
Whole house iron filter

Rotten egg smell

Hydrogen sulfide

Manganese Greensand filter

Water has laxative effect

Excess sulfates

Reverse Osmosis

Water is gritty, muddy, or appears dirty

Excess sand, dirt, or other sediments in your water

Whole House Sediment Filter
Any point-of-use filter system with a sediment filter