What Do Water Filters Remove?

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Potential Water Contaminants and the Systems Designed to Remove Them

Before you begin shopping for a water filtration system for your home, not only will you want to know what is in your water to begin with, but you also will want to know which contaminant is removed by which type of system.

We’ll list the major concerns that most consumers have on this page, along with the types of systems designed to treat them. Remember, this is only a general guideline. While we do our best to identify the most commonly mentioned potential contaminants or other substances that you may find objectionable in your water, this is just a partial list.

For example, while we mention volatile organic compounds (VOCs), we do not itemize each compound. An official document regarding this and other contaminants is located at the National Public Health and Safety Organization. 1

Remember that no single water filtration system is designed to remove every contaminant.

Partial List of What Granular Activated Carbon Water Filters Remove 2

Note that the substances in the following table are primarily “chemicals” – including Volatile Organic Chemicals (VOCs) unless otherwise noted (e.g. Cobalt is a radiological substance). Also, note that Granular Activated Carbon (GAC) filters do not remove viruses.

1,2,3-TrichloropropaneBenzeneDichlorvosMethomylRadium (Radiological)
1,3,5-trinitroperhydro-1,3,5-triazine (RDX)Calicivirus (microbial)DicrotophosMetolachlorSaxitoxin (Microbial)
1,4-dioxaneCarbofuranEthylene DibromideMetolachlor DegradatesSimazine (including Simazine Degradates – pesticides and herbicides such as Simadex, Aquazine, Gesatop and more -see footnote 3 below)
17a-ethynyl estradiolChlorine odorFulvic acidMicrocystinsStrychnine (a poison used in rodent control products; see the footnote 3 below
4-NonylphenolChlortetracyclineHumic acidNatural Organic Matter (See full list at the EPA page listed in footnote 3 below)Sulfur odor
Ammonium perchlorateCobalt (radiological)Methyl tertiary-butyl ether, methyl-t-butyl ether – aka MTBEParticulates and SedimentsTetrachloroethylene
Arsenic (how much it reduces depends on the filter – check with the manufacturer)Cryptosporidium (microbial)Mercury (check with each manufacturer – some levels of mercury may be too high to remove with a standard filter)2Perfluorooctane Sulfonate (See full list at the EPA page listed in footnote 3 below)Trichloroethylene

Again, please note that this is not an all inclusive list. Refer to each manufacturer because not all filters are created equal!

Contaminants Removed by Reverse Osmosis

As is the case with any filter, please remember to check with the manufacturer regarding whether or not a substance will be removed by the system you are considering. Also, remember that with RO water filtration systems, it is helpful that one of the steps include a carbon filter to remove some of the substances that the RO membranes alone may not. Again, this table is compiled from numerous resources noted in the footnotes below this article.

ArsenicChromiumNitratesRadium
Bacteria and viruses – most disease-causing organisms such as
Campylobacter, E. coli, Salmonella, and Shigella and viruses
such as Enteric, Hepatitis A, Norovirus, and Rotavirus
CopperPotassiumSodium
CalciumFluoridePhosphorousSulfate
ChlorideLeadProtozoa such as
Cryptosporidium and Giardia

Reverse Osmosis remains one of the most popular and most effective methods for filtering your water, and there are many options available from whole house to point-of-use (e.g. countertop) installation.

What Does Distillation Remove From Water?

One of the more specific questions we have been asked with regard to water distillation is, “Does distilling water remove fluoride and chlorine?” If you find these substances to be objectionable, you will be pleased to know that yes, distillation does remove fluoride as well as chlorine.

It removes a lot more too – in particular, soluble minerals, as the following list indicates, however it won’t take out chemicals whose boiling points are near or lower than that of water (especially VOCs that boil at about 207-218 degrees Fahrenheit) because those will “travel” with the vaporizing liquid into the collection vessel at the other end of the process. If these are an issue for you, and you would still like to use distillation as a filtration method, consider purchasing a unit with an added carbon filter option. The following table illustrates what can be removed by distillation:4

ArsenicLead
Calcium (actually pretty much all soluble minerals, leaving
the water tasting “bland” or “flat” – but these are also considered
“hardness” elements)
Magnesium (another “hardness” substance)
ChlorineMercury
FluorideNitrate
IronPhosphorous

Note that when it comes to microorganisms (like bacteria, protozoa, and viruses), because the distillation process includes boiling, those nasties are pretty effectively “inactivated.” This comes with a caution, however, because if you don’t use your distiller for a while, these substances can always be re-introduced and re-contaminate your water.

Contaminants Removed by Ion Exchange Water Filters

Remember that in an Ion Exchange (IE) filtration system, you will be “exchanging” one ion for another. These systems are most commonly known as ion exchange water softeners – or rather, ion exchange is the conventional way in which household water softeners work.5 In most cases the substance that is reintroduced to the water after the exchange will be sodium ions.

This table lists the primary substances that you can expect to be removed from your water via ion exchange:6, 7, 8

ArsenicMagnesium
BariumNitrates
CalciumRadium
FluorideSulfate
IronUranium
Manganese

The very process of water softening means that the “hardness” minerals must be removed – and in the process are “attracted” to the negatively-charged resins, after which, the “soft” (and positively-charged) sodium ions replace them. In a water conditioning system, however, there are salt-free options – but note that this will not be “soft water,” but “conditioned.

Footnotes and Sources Used in the preparation of this report.

1 www.nsf.org/consumer-resources/water-quality/water-filters-testing-treatment/contaminant-reduction-claims-guide

2 people.uwec.edu/piercech/hg/mercury_water/removalmercury.htm

For a full list of what Granular Activated Carbon filtration systems remove, visit the Environmental Protection Agency page at iaspub.epa.gov/tdb/pages/treatment/treatmentOverview.do?treatmentProcessId=2074826383

4 www.iwapublishing.com/news/distillation-treatment-and-removal-contaminants-drinking-water

5 en.wikipedia.org/wiki/Water_softening

6 www.epa.gov/sites/production/files/2015-11/documents/2005_11_17_faq_fs_healthseries_filtration.pdf

7 cfpub.epa.gov/safewater/radionuclides/radionuclides.cfm?action=Rad_Ion%20Exchange (Note, this also explains drawbacks of Ion Exchange)

8  https://iaspub.epa.gov/tdb/pages/treatment/treatmentOverview.do?treatmentProcessId=263654386

Other sources:

extensionpublications.unl.edu/assets/html/g1493/build/g1493.htm

www.cdc.gov/healthywater/drinking/home-water-treatment/household_water_treatment.html