Water Filter Types (and the Gross Contaminants They Remove)

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Household water quality isn't always what we hope it would be, but on the bright side, a water filter may be all that's needed to clear out any contaminants. The tricky part is deciding exactly which filter types and designs are best for your needs since one water filter is completely different from the next. Some excel at removing contaminants like lead or asbestos, while others kill bacteria. Still others do little more than make the water taste better by removing chlorine or fluoride.


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The right water filter for your home depends on both what you expect from it and where you'd like to use it. A whole-home filtration system cleans the water in the entire house, but it's not a cost-effective option in many cases. If your goal is simply to have better-tasting tap water, any one of several kitchen-based water filters may be the better choice.

Reverse Osmosis Filters

Reverse osmosis (or RO) filters remove metals and other impurities from water. Once connected to a water line in your home, an RO filtration setup uses a pressurized pump to push the water through a semipermeable membrane at one of the final stages of the filtration process. The downside to RO filters is that they use a lot of water in order to function properly, so they typically aren't used in whole-house water filtration systems, but they are often connected to a kitchen sink or as part of a filtering water pitcher. In many cases, for a whole-home RO system, it takes 2 gallons of water to produce 1 gallon of filtered water, which would mean doubling the water bill.

Revers osmosis systems typically use a series of different filters, or prefilters, rather than reverse osmosis alone. The water in the line connected to the filtration system goes through several different filters to remove impurities, such as chlorine or lead, and then through a special semipermeable membrane for the reverse osmosis stage. This membrane lets very few contaminants through. Some RO filtration systems have yet another filter after the reverse osmosis stage.

Quality RO and other types of water filters are certified by NSF International as to which contaminants each filter specifically removes. As with other types of filters, read the product information and look for the NSF certification information on the package to ensure that the filter removes what the manufacturer claims. RO filters typically remove substances such as copper, fluoride, chlorine, and lead as well as nitrates, pesticides, or residual pharmaceuticals in the water supply. This process often improves the taste of drinking water.


Ultraviolet Light Filters

Ultraviolet, or UV, light filters remove some types of germs from the water, which also helps lower the risk of water-borne illnesses. This type of filtration works by exposing the water to certain UV light frequencies that disrupt the DNA of microorganisms, which ultimately prevents the spread of some illnesses and diseases. UV filters remove E. coli, salmonella, and cholera from the water among other contaminants as well as some forms of algae and fungi. While UV filters do an excellent job of destroying germs, they don't remove other forms of contaminants, such as metals or chemicals.

An ultraviolet light water filtration system is a good idea if your home has poor water quality or if your water source is a well and the water is known to contain microorganisms or germs that could lead to illness. In most municipal water systems, chlorine kills a majority of the types of germs or parasites that may otherwise live in the water, but some parasites, such as cryptosporidium, aren't affected by the levels of chlorine used in municipal water supplies.

If this type of parasite passes through to your home's water supply, this means it also gets into your tap water. If you drink tap water containing such a parasite, you could experience stomach discomfort or other issues. If you suspect your tap water is unhealthy to drink due to microorganisms, UV filtration could solve the problem. Running such water through both a reverse-osmosis filter and a UV filter is an even better way to ensure the pathogens are removed. Some water purification systems offer multiple forms of filtration, so shop around to ensure you're getting the most bang for the buck if you have tap water or a less than ideal municipal water system.

Activated Carbon Filters

Activated carbon, sometimes called activated charcoal, is one of the most common filter types, especially for drinking water. This technology uses charcoal— a charred, porous material — as the filter that captures certain contaminants in the water by binding to those substances. Exactly what they filter out varies from one carbon filter to the next. Some remove chlorine, which helps improve the taste of tap water, while others remove substances such as lead and mercury or even pesticides. Be sure the product is rated by NSF International to remove specific contaminants rather than just assuming the filter removes every type of contaminant that may be in the water.


The pore size on a carbon filter determines how good a job the filter does at removing contaminants. As with sifting rocks, a screen with large holes in it allows all kinds of material through, while the smallest screen or filter size prevents all but the tiniest particles from passing through the material. The best carbon filters have a screen size of less than 1 micron, as the filter screens out additional substances that aren't removed by the activated carbon itself.

Carbon water filters and any other type of water filtration relying on screens or materials to catch contaminants have to be replaced from time to time in order to remain effective. Exactly how often you need to replace the filter depends on the type of filter and how it's used. For instance, a carbon filter in a water pitcher may have to be replaced every few months if you use the pitcher daily. Consult your product's literature to determine how often to replace the filter. For best results, purchase a few extras long before you need them and schedule the filter-changing dates on a calendar.

Ion Exchange Filters

An ion exchange water filter uses a special resin that attracts one type of ion and swaps it for another, such as taking the magnesium and calcium ions out of the water and replacing them with sodium ions, effectively softening the water. This type of filtration comes in handy where hard water, or excessive mineral content, is an issue, and it's often installed as a whole-home setup. Some ion exchange filters remove radium, barium, and fluoride as well. Ion exchange filters don't remove germs and generally don't remove other contaminants, such as chemicals, from the water. As with any filters, look for NSF certification to find out what any specific ion exchange filter really removes.

In most cases, ion exchange filters are not necessary unless hard water is so much an issue that it leaves mineral deposits on dishes and glassware or if everyone in the home suffers from dry skin and hair due to the minerals in the water. A water-softening ion exchange system also leaves a little salt in the home's water, which could be an issue for those watching their daily sodium intake.


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Do I Need Whole-House Filtration?

As its name implies, a whole-house water filter removes contaminants from the entire water supply reaching your house, which means the water from any tap, shower, or even the outdoor spigots comes out cleaner than it was before it reached your house. These are sometimes called point-of-entry filters, as they connect to the main water line entering your house. As with smaller, more affordable water filtration systems, whole-house water filters don't all remove the same contaminants, so it's important to read the product literature if your goal is to remove metals, chemicals, or bacteria and germs, for instance.

A whole-house water filter system is a major expense that could also mean significant modifications to your home's plumbing, as it requires connecting it to the main water supply in your home. If your whole-home filter removes chlorine from the water, germs may eventually thrive within your home's pipes since there's no chemical acting against them on a regular basis if they've found a way into the pipes. This could be an issue if you don't change the filter regularly or about every six to 12 months depending on the model and your water usage. Changing the filter is a bit of a project, as it requires shutting off the water to the entire home and releasing pressure (and sometimes excess water) before installing the new filter cartridge.

Smaller Setups to Remove Contaminants

There's no need to use a whole-house filter if all you really need is cleaner water in the kitchen. The kitchen sink is a good place for a water filter, with options ranging from simple models that screw onto the end of the spout to more elaborate point-of-use filters that fit under the sink or even on the countertop. Point-of-use filters install for use on a specific water line, such as the kitchen or bathroom sink. These are often installed under the sink. Reverse osmosis is one of the most common filter types for point-of-use filtration.


Countertop water filters are another option, and these sit on the countertop with the filter inside the countertop filter housing. Many of these install on the spout by removing the sink spout's aerator and attaching the filter's diverter, a hose, and optionally, some gaskets and adapters to ensure a proper fit. A countertop bottleless water cooler is another option that usually includes RO and possibly other types of filtration. Some of these offer options to heat or cool the water or serve it at room temperature. This type of design with built-in cooling and optional heating costs more than the attach-to-the-sink type of countertop filter, and it's more difficult to install, as it requires tapping into the water and drain lines, which may be reason to call a plumber.

Other point-of-use water filters install beneath a kitchen or bathroom sink, often requiring a separate hole through the sink or countertop to install a separate spout for the filtered water. This type of setup also requires tapping into the cold water line under the sink and modifying it to provide water to both the original sink spout and the new filtered-water spout, which could mean a project for a plumber if you're not comfortable doing the work yourself. The simplest and often least expensive water filters of all are the pitcher style that has the filter built into the lid or elsewhere in the container. These require replacing the filter every few months to ensure optimal filtration, but as with any filter, read the certifications and product literature to ensure a quality product that filters out the contaminants on your target list.



Kathy Adams is an award-winning writer. She is an avid DIYer that is equally at home repurposing random objects into new, useful creations as she is at supporting community gardening efforts and writing about healthy alternatives to household chemicals. She's written numerous DIY articles for paint and decor companies, as well as for Black + Decker, Hunker, SFGate, Landlordology and others.