Water Filter Contaminant Removal Chart: What Each Filter Type Removes

Water filtration systems vary significantly in which contaminants they remove, and selecting the wrong technology for a given water chemistry profile can leave regulated contaminants at levels above EPA Maximum Contaminant Levels (MCLs). This page maps the principal filter technologies — reverse osmosis, activated carbon, ion exchange, ceramic, UV, and ultrafiltration — against their documented removal capabilities, the standards under which those claims are validated, and the structural conditions that determine where each technology is appropriate. The Water Filtration Listings directory covers licensed service providers who install and certify these systems.

Definition and scope

A water filter contaminant removal chart is a reference matrix that correlates filter media or technology type with the classes of contaminants each is engineered to reduce or eliminate. The scope of legitimate removal claims is bounded by third-party certification: NSF International and the American National Standards Institute (ANSI) jointly publish standards — most notably NSF/ANSI 42, NSF/ANSI 53, NSF/ANSI 58, and NSF/ANSI 55 — that define the testing protocols, challenge concentrations, and minimum reduction percentages required for each contaminant class.

The U.S. Environmental Protection Agency (EPA) sets enforceable MCLs for 90+ regulated contaminants under the Safe Drinking Water Act (SDWA), which defines the regulatory floor that point-of-entry and point-of-use systems must account for. Contaminant classes under the SDWA include microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, and radionuclides. Filter selection must be matched to the contaminant classes present in a specific water source — a determination made through laboratory water testing, not manufacturer marketing materials.

The Water Filtration Authority directory purpose and scope outlines how this resource is organized within the broader framework of licensed plumbing service sectors.

How it works

Each filter technology operates through a distinct physical or chemical mechanism, which directly determines what it can and cannot remove:

1. Activated Carbon (AC/GAC/Block Carbon): Adsorption — contaminant molecules bind to the porous carbon surface. Effective against chlorine, chloramines, volatile organic compounds (VOCs), trihalomethanes (THMs), certain pesticides, and taste/odor compounds. Certified under NSF/ANSI 42 (aesthetic effects) and NSF/ANSI 53 (health effects). Does not remove dissolved minerals, heavy metals in ionic form (unless specialized catalytic carbon is used), nitrates, fluoride, or microbiological contaminants without additional treatment stages.

2. Reverse Osmosis (RO): Pressure-driven membrane separation — water is forced through a semi-permeable membrane with pore sizes typically between 0.0001 and 0.001 microns. Removes dissolved salts, heavy metals (lead, arsenic, chromium-6), nitrates, fluoride, perchlorate, and most inorganic contaminants. Certified under NSF/ANSI 58. RO systems reject 90–99% of dissolved solids depending on membrane condition, feed water pressure (typically 40–80 psi minimum), and temperature. Produces a reject (brine) stream of 3–4 gallons of wastewater per gallon of product water in standard residential configurations.

3. Ion Exchange (IX) — Cation/Anion Resin: Chemical exchange of ions in solution for less harmful ions bound to resin beads. Water softeners use sodium-form cation resin to replace calcium and magnesium ions (hardness). Specialized anion resins target nitrate, arsenic (V), chromate, and perchlorate. Does not remove pathogens, sediment, or most organic compounds. Certified under NSF/ANSI 44 for softeners and NSF/ANSI 61 for system materials.

4. Ceramic Filtration: Physical size exclusion through a porous ceramic matrix, typically with pore sizes of 0.5–1.0 microns. Removes sediment, turbidity, cysts (Cryptosporidium, Giardia), and some bacteria. Does not remove viruses, dissolved chemicals, or heavy metals unless impregnated with silver (bacteriostatic only) or paired with a secondary media.

5. Ultraviolet (UV) Disinfection: Photochemical disruption — UV-C radiation at 254 nanometers damages the DNA and RNA of microorganisms, rendering them unable to reproduce. Effective against bacteria, viruses, and protozoa when UV dose reaches 40 mJ/cm² (the standard set by NSF/ANSI 55 Class A). Does not remove any chemical contaminants, sediment, or dissolved solids. Requires pre-filtration to below 1 NTU turbidity for effective pathogen inactivation.

6. Ultrafiltration (UF): Membrane filtration at 0.01–0.1 micron pore size. Removes bacteria, cysts, colloidal particles, and some viruses. Does not remove dissolved inorganic contaminants, heavy metals, or small organic molecules. Often paired with activated carbon in multi-stage systems.

Common scenarios

Lead contamination (plumbing corrosion): Certified RO systems and NSF/ANSI 53-certified solid block carbon filters both carry verified lead reduction claims. The EPA Lead and Copper Rule (LCR) identifies lead from service lines and premise plumbing as the primary residential exposure pathway. RO reduces lead by 95%+ at point-of-use; carbon block certified to NSF/ANSI 53 reduces lead by ≥99% at tested flow rates.

Nitrate in agricultural regions: Ion exchange with anion resin or RO are the two technologies with validated nitrate reduction claims under NSF/ANSI 58 and NSF/ANSI 44. The EPA MCL for nitrate is 10 mg/L as nitrogen (EPA SDWA contaminant tables). Activated carbon provides negligible nitrate reduction and is not an appropriate primary technology for this contaminant class.

Private well water with biological risk: UV disinfection rated to NSF/ANSI 55 Class A, combined with a 1-micron pre-filter and a ceramic or UF stage, addresses the full microbiological risk profile (bacteria, viruses, cysts). Single-technology carbon or sediment filtration does not meet this profile.

Disinfection byproducts (THMs, HAAs) in municipal water: Activated carbon — particularly granular activated carbon (GAC) meeting NSF/ANSI 53 — is the primary documented technology for THM and haloacetic acid (HAA) reduction. The EPA regulates THMs under the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) with an MCL of 80 µg/L for total THMs.

Decision boundaries

The choice between filter technologies follows hard technical boundaries, not preference:

Carbon vs. RO: Activated carbon is the correct technology for organic chemical reduction (VOCs, THMs, pesticides) and costs substantially less to operate, but it cannot address dissolved inorganic contaminants at MCL-relevant concentrations. RO systems address a broader inorganic contaminant profile at the cost of higher wastewater ratios and installation complexity, including drain line access and minimum feed pressure requirements.

UV vs. Chemical disinfection: UV provides no residual disinfection protection downstream of the treatment point