In this page the various types of water filtration systems currently used are discussed.

Activated Carbon Filters


Activated Carbon (Image Courtesy: Wikipedia.org)

Activated Carbon (Image Courtesy: Wikipedia.org)


Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.

Activated carbon filters adsorb organic contaminants that cause taste and odor problems. Depending on their design, some units can remove chlorination byproducts, some cleaning solvents, and pesticides.

To maintain the effectiveness of these units, the carbon canisters must be replaced periodically. Activated carbon filters are efficient in removing metals such as lead and copper if they are designed to absorb or remove lead.

Ion Exchange Filters


Ion Exchange Filter

Ion Exchange Filtration. Image Courtesy: http://www.vccs.edu/

Because ion exchange units can be used to remove minerals from your water, particularly calcium and magnesium, they are sold for water softening. Some ion exchange softening units remove radium and barium from water. Ion exchange systems that employ activated alumina are used to remove fluoride and arsenate from water. These units must be regenerated periodically with salt.

Ion exchange softening is described as effective for water containing less than 2-5 mg/L of dissolved iron and manganese. Ion exchange will not work at all where the iron and manganese have turned to a rusty color. Other aspects of water quality such as pH or alkalinity are not important in the operation of ion exchange.

Reverse Osmosis Filters

Reverse Osmosis Filter

Reverse Osmosis Filters. Image Courtesy: http://www.unl.edu/

Reverse osmosis treatment units generally remove a more diverse list of contaminants than other systems. They can remove nitrates, sodium, other dissolved inorganics, and organic compounds.

The movement of water from soil into plant roots is an example of osmosis at work in nature. Now a days, reverse osmosis is becoming a common home treatment method for contaminated drinking water.

The simplest home Reverse Osmosis Filtration system consists of a semi-porous membrane, a storage container for the treated water, and a flow regulator and valve to back-flush the membrane when it becomes clogged. Tap water is passed through a membrane that filters out most of the contaminants. Eventually, the pores of the membrane become clogged with minerals and the flow-through of water slows down. To remove these residues, the membrane is back-flushed using tap water, which creates reject water high in salts. This brackish water is automatically discharged into the home drain system.

Distillation Filters


Distillation units boil water and condense the resulting steam to create distilled water. Depending on their design, some of these units may allow vaporized organic contaminants to condense back into the product water, thus minimizing the removal of organics. You may choose to boil your water to remove microbial contaminants. Keep in mind that boiling reduces the volume of water by about 20 percent, thus concentrating those contaminants not affected by the temperature of boiling water, such as nitrates and Pesticides.

No one unit can remove everything. Have your water tested by a certified laboratory prior to purchasing any device. Do not rely on the tests conducted by salespeople that want to sell you their product.

The below table shows the comparison of various water filtration technologies (Source: EPA)

Water Treatment Methods
Method What It Does to Water Treatment Limitations
Activated Carbon Filters (includes mixed media that remove heavy metals) Adsorbs organic contaminants that cause taste and odor problems. Is efficient in removing metals such as lead and copper.
Some designs remove chlorination byproducts. Does not remove nitrate, bacteria or dissolved minerals.
Some types remove cleaning solvents and pestisides.
Ion Exchange Filters (with activated alumina) Removes minerals, particularly calcium and magnesium that make water “hard.” If water has oxidized iron or iron bacteria, the ion-exchange resin will become coated or clogged and lose its softening ability.
Some designs remove radium and barium.
Removes fluoride.
Reverse Osmosis Filters (with carbon) Removes nitrates, sodium, other dissolved inorganics and organic compounds.
Removes foul tastes, smells or colors.
May also reduce the level of some pesticides, dioxins and chloroform and petrochemicals.
Distillation Filters Removes nitrates, bacteria, sodium, hardness, dissolved solids, most organic compounds, heavy metals, and radionucleides. Does not remove some volatile organic contaminants, certain pesticides and volatile solvents.
Kills bacteria. Bacteria may recolonize on the cooling coils during inactive periods.