Water Filters

Filling glass of tap water

Designed to remove or reduce contaminants from water used for drinking, cooking, washing and showering, a water filter is, on the one hand, a far more cost-effective solution than bottled water.

On the other hand, water filters provide a measure of protection against the potentially harmful effects of chemicals, heavy metals and microorganisms.

Water filters come in many types both in terms of the system and filter media used. While specifications, performance and cost vary widely, the application of water filters is essentially the same no matter what the system.

Water Filter Systems

Many types of water filtration systems are available for both consumer and commercial application. In lieu of the fact that more and more contaminants, including pharmaceuticals, inorganic solids and pathogens, find their ways into water supplies, homeowners, renters and businesses alike realize the value of an effective water filter.

Each system comes with its own set of specifications regarding compatibility, installation and maintenance. At minimum, a water filtration system includes a filter housing and replaceable cartridge. Portable systems include a receptacle to store filtered water.

Countertop, under-sink and refrigerator systems use their own faucet or dispenser to deliver filtered water, while faucet-mounted, inline and whole-house systems rely upon an existing tap.

Water filters may be point-of-use or point-of-entry systems. With the exception of whole-house filters, all types listed are point-of-use systems, meaning that water is filtered in the same place it is dispensed.

Water Filter Media

In addition to the type of system in place, the type of filter media used within the system is another major distinction. The term "filter media" describes the materials or substances used to filter water. In the home, the primary media used include carbon, metal alloys, reverse osmosis and ceramic.

Other media include ultraviolet light, ion exchange resin, pleated paper and spun polypropylene fiber. Of all types, carbon-based filter media are the most common.

Carbon Media Water Filters

Two main varieties of carbon media are used in water filters: carbon block and granular-activated carbon. A carbon block filter is a densely packed, near-solid piece of activated charcoal commonly made from the husks of coconuts. Granular-activated carbon or GAC filters are less dense, featuring instead a quantity of sand-sized carbon granules.

A small amount of carbon contains a very large surface area owing to its physical properties. Carbon filters are very effective, for unfiltered water has a lot of area to come into contact with.

Metal Alloy Water Filters

Metal alloy filters, such as KDF-55, use a bed of granulated copper and zinc to create zinc oxide, which inhibits the growth of bacteria. Also called redox filters because of the process of oxidation reduction, KDF and other metal alloy filters are commonly used in conjunction with other filters during multistage filtration processes.

Reverse Osmosis Water Filters

Reverse osmosis or RO filtration systems use a multistage process, at the center of which is a membrane module. Through the application of pressure, contaminated water is separated from clean water which is allowed to pass through a microporous filter or membrane that traps nearly everything except water molecules.

Ceramic Water Filters

Ceramic water filters, commonly impregnated with nano-silver particles, excel at removing microorganisms and other impurities from water. Essentially consisting of a fossilized element, the microporous ceramic media can stop particles as small as 1/100,000th of an inch or 0.22 microns.

Other Filters

Water ionizers use a magnetic field to divide water into dual streams, one of which is alkaline-rich and ideal for consumption, the other being acid-rich and usually discarded. UV filters use an ultraviolet light to destroy virtually all living organisms that may be present in water.

Ion exchange filters can remove inorganic solids and soften water, but they are ineffective at removing chemicals and bacteria.

Pleated paper and spun polypropylene filters are effective at removing only sediment, sand, rust and other larger debris particles from water. These filters are used only as pre-filters designed to prevent damage to water systems, appliances and other filters.


The most important aspect of any filtration system, filter type or method is what it removes from water to make it safer for consumption. Commonly found in tap water are a great many chemicals, heavy metals, microorganisms and organic compounds that have the potential to cause sickness.

High contaminant levels in drinking water can cause long-term health problems and skin irritation (when showering) and can be harmful to people with compromised immune systems. A short list of contaminants that may be in tap water includes:

  • Chlorination byproducts
  • Lead
  • Mercury
  • Chromium
  • Copper
  • Cadmium
  • Asbestos
  • Volatile organic compounds (VOCs like benzene, et al)
  • Viruses
  • Bacteriological organisms
  • Herbicides
  • Pesticides
  • Sediment
  • Rust

Seldom does a single filter media type remove all possible contaminants. For this reason, multistage filtration systems with as many as 10 stages are used. Water first passes through a pre-filter designed to remove large particles like sediment.

From there, water becomes progressively more filtered as it passes through a combination that may include redox media, multiple carbon stages, ion exchange media, a membrane module and ultraviolet light.

Contaminant removal is measured as a percentage. Thus, a filter may reduce chlorine odor and taste by 98 percent or remove 99.99 percent of microbial cysts. Filters are tested by the NSF and/or ANSI and certified to meet certain standards.

Carbon filters have a life of 3 to 6 months before they need replacing. Ceramic filters and membrane modules can be scrubbed and, consequently, last longer.


Depending on the water filter system, installation will differ. Portable systems require no installation, for they are fully self-contained. Faucet-mounted filters attach to virtually any kitchen faucet in seconds without any tools.

Under-sink and countertop systems require a more complicated installation to mount the filter housing, install the dedicated faucet and connect to the water line.

Whole-house systems must be installed at the point of entry into a house. Refrigerator filters are very easy to remove and replace, for the system comes pre-built into certain refrigerator models. Inline filters are an exception to this. They connect directly to the water line feeding any refrigerator water dispenser.

Portable water filtration systems start as low as $10 but can cost $500 or more for highly advanced units. Faucet-mounted, countertop, under-sink and whole-house systems range in price from $20 to several hundreds or thousands of dollars.

Equipping a home or business with a water filter does not have to be terribly expensive, although routine cleaning and/or maintenance of the filtration system is required. Water filter cartridges must be replaced upon expiration in order for the system to remain effective.

Water Filter Necessity

The United States in general has high water quality standards and most of the water that comes out of our home water taps is clean and pure. However, even clean and pure water can have odors or appear cloudy, characteristics a water filtration system can improve.

In fact, a home water filter system can rectify the overall appearance, taste and smell of tap water, plus remove some chemical contaminants in the water. If you'd like to improve some aspects of your home's drinking water, here's some basic information on home water filters.

Two Home Water Filter Designs

Point of use devices are small appliances designed to treat washing and drinking water. They’re usually installed on a tap, but can simply be pitchers where water is poured into the top then works it’s way down thorough a filter by gravity.

Point of entry devices are larger units installed onto a homes water supply and they filter all the water entering a home. Since these units are designed to treat larger volumes of water point of entry filters need to be plumbed into the home’s water system (making them more costly than point of use filters).

Particle Filters

These designs use a membrane or screen to trap particles suspended in the water and filter them out. Their filtering capability depends on the size of the openings in the membrane (measured in microns or millionths of an inch). The lower the number of microns, the smaller the openings in the pores and the more effective the filter.

Particle filters are commonly made from either fiber ( rayon or cellulose) or ceramics, that trap particles of dirt, floating fibers, as well as some bacteria and parasites (although not enough to purify the water). They won’t remove any dissolved chemical contaminants.
Activated Carbon (AC) filters

AC carbon filters are effective at improving the taste, appearance and odor of water because they are effective at removing the organic contaminants that cause these problems.

'There are two types of AC filters, Granular Activated Carbon filters that use a cartridge packed with carbon granules and Solid-Block Activated Carbon filters that (not surprisingly) uses carbon in a block form.

With either type of carbon filter, the carbon granules or the small pores in the carbon block trap particles and absorb substances dissolved in the water, like chlorine, metal or pesticides.

Resin Filters

Use resins to remove contaminants and minerals that cause deposits to from in water pipes and on appliances such as coffeepots.

Resin filters are sometime combined with Carbon Activated Filters to provide ‘double filtering’ of water to better remove both dissolved chemical substances and particles.

Should You Get a Water Filter?

If you’re concerned about the quality of your tap water, boiling before drinking is the best way to ensure there are no living microorganisms in it.

However, if you find your water has a flavor your don’t like, appears cloudy or dirty or has a nasty odor, a water filter will definitely improve it.

Home water filters are designed for use with micro biologically safe water and no single water filter can remove all types of substances from water, so you may need to look at a few to find one that can address your particular concern. However, the good news is water filters are generally labeled and tell you what they will remove.