What is Water Filtering?

Aug. 24, 2021

Water filtering is a method used to filter out undesired chemical compounds, organic and inorganic materials, and biological contaminants from water. The purpose of water filtration is to provide clean drinking water.

About the author:

Cristina Tuser is associate editor for WWD. Tuser can be reached at [email protected].

What is water filtering?

Water purification takes place on small and large scales, and water filtering can provide clean and potable water for industrial applications, in addition to individual households. 

The filtration process reduces the concentration of contaminants such as: suspended particles, parasites, bacteria, algae, viruses, and fungi. 

Why water filtration is important

It is virtually impossible to determine water quality on the basis of appearance. Multiple processes—such as physical, chemical, or biological analyses—have been developed to test contamination levels. Levels of organic and inorganic chemicals are some of the common parameters analyzed to determine water quality and contamination levels.

Tap water is often filtered in a water purification facility before it reaches the end user. Nevertheless, authorities test the water quality right after the water is filtered, before it goes in the municipal feed lines, which generally produces results above the required standard. What remains unaccounted for is the age of the feed lines and their length, however.

It is not uncommon for the pipes to be decades old, and by traveling a long time through them, filtered water can become polluted with everything it encounters along the way. Old pipes can redistribute microorganisms, bacteria, and viruses, as was the case in Flint, Michigan Crisis, and Chicago in regards to lead pipe. In the event that water is not filtered, the likelihood of exposure to harmful contaminants increases. 

For instance, there is evidence that exposure to per- and polyfluoroalkyl substances (PFAS) can lead to adverse health outcomes in humans. The U.S. EPA reports that if humans or animals ingest PFAS, over time the contaminants can accumulate in the body. Exposure can lead humans to suffer from adverse health effects such as: a weakened immune system, cancer and thyroid hormone disruption.

How do you select a water filter?

The selection of specific water filtering processes depends upon factors such as; intake water quality; degree of purification required; intended water use; flow capacity requirements; government regulations; available capital; and the operations and maintenance costs involved.

Common water filtration methods

Activated Carbon & Granular Activated Carbon (GAC)

The activated carbon filtration method relies on adsorption. Molecules in the water are trapped in the porous structure of a carbon substrate. Activated charcoal filters remove sediment, chlorine, and volatile organic compounds (VOCs). Carbon filtration is not as effective at removing salts, minerals and dissolved inorganic compounds, however.

There are also two types of carbon filters used for water filtering: powdered block filters and the granular activated carbon (GAC) filters

Carbon block filters offer a larger adsorption surface and many of them have additional layers in between the carbon for a better filtration. Some even possess silver layers that will block bacteria and prevent bacteria growth.

GAC filters come in various sizes and use finer granulated charcoal that has a smaller surface area than the carbon block, which can produce a channeling effect.

Bacterial colonies can grow inside the filter if it is not used for a long time, even if it’s treated.


Ion Exchange Filters & Deionization (DI)

Deionization (DI) is the chemical process of removing dissolved impurities, or ions, from water. Ion exchange neutralizes ions with other ions and is suitable for relatively low concentrations of impurities. Although deionization produces a pure, high quality of water, it is typically ineffective against organic pollutants. 

Deionization filters use beads charged with hydrogen ions and hydroxyl ions and change them for cations and anions. When metallic ions enter the filter, the hydrogen is released and replaces the metals, which get trapped in the beads. The anions originally in the water are exchanged with the hydroxyl ions, then the hydrogen and the hydroxyl combine. The end product is mineral-free water.

Similarly, water softening systems work by exchanging the salt trapped in the beads with the magnesium and calcium ions. Salt is released while the minerals are trapped, thus making the water softer. 

Industrial water softening effectively reduces or eliminates scale build-up in boilers, valves and other equipment. This reduces costs by extending the life of filters and equipment, ultimately reducing maintenance expenses.


Distillation is one of the simplest ways to filter water. Water is boiled and the condensed steam is captured in a separate container. All the contaminants remaining in the original container then are removed. Some contaminants can reach a boil before the water, and are still present in the second tank, however.


Reverse Osmosis (RO)

Reverse osmosis (RO) uses multiple filters to remove the contaminants. Typically, the first filter is a mechanical one, the second and third filters are made out of carbon, the fourth is the semi-permeable membrane, and the fifth is a chemical one.

RELATED: What is Reverse Osmosis (RO)?

RO is the preferred water filtering method for higher concentrations of impurities. RO water filtration systems force water through a semipermeable filter under high pressure. The filter then permits the water, but not the contaminants, to pass through.

RO is one of the most effective water filtration methods for removing bacteria and viruses from water.

About the Author

Cristina Tuser

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