Under-Sink with Dedicated FaucetAlso: Countertop Standalone System · Commercial Whole-Home (rare, high cost)
Reverse Osmosis (RO)
- NSF/ANSI 58Reverse Osmosis Drinking Water Treatment Systems
Water is forced under domestic line pressure across a dense semi-permeable polyamide thin-film composite (TFC) membrane. Contaminants larger than water molecules are rejected and flushed to the drain line, producing high-purity permeate water.
Effective forPFASMetalsDisinfection by-productsRadionuclidesWater characteristicsVOCs
LimitationDischarges 1 to 3 gallons of brine wastewater for every gallon of purified water produced
Under-Sink In-LineAlso: Countertop · Gravity Pitcher · Faucet Mount · Whole-House Main Line
Activated Carbon Filtration (Solid Block / GAC)
- NSF/ANSI 42Aesthetic Effects: Chlorine Taste & Odor
- NSF/ANSI 53Health Effects: VOCs, Lead, PFOA/PFOS Adsorption
- NSF/ANSI 401Emerging Compounds & Pharmaceuticals
Utilizes high-surface-area activated coconut shell or bituminous coal carbon. Contaminant molecules adhere to the extensive internal micro-pore structure through physical and chemical adsorption (Van der Waals forces). Catalytic formulations accelerate chloramine breakdown.
Effective forDisinfection by-productsVOCsPFAS
LimitationIneffective for dissolved inorganic minerals, nitrate, arsenic, or hardness salts
Point-of-Entry Whole-HouseAlso: Under-Sink Specialty Canister
Ion Exchange (Specialized Resins)
- NSF/ANSI 61Drinking Water System Components
- NSF/ANSI 53Specific Inorganic Contaminants
Water flows through a tank or cartridge packed with microscopic polymer resin beads loaded with exchangeable ions (e.g., chloride or sodium). As water passes, target ions (such as negatively charged arsenate, nitrate, or cationic heavy metals) exhibit higher chemical affinity and displace the resin ions.
Effective forMetalsRadionuclidesWater characteristics
LimitationRequires periodic regeneration with brine solution or regular disposable cartridge swaps
Point-of-Entry Whole-House only
Cation Exchange Water Softening
- NSF/ANSI 44Residential Cation Exchange Water Softeners
Hard water passes over strong acid cation (SAC) resin beads saturated with sodium ions. The resin captures calcium and magnesium ions and releases an equivalent ionic charge of sodium. A periodic brine backwash regenerates the beads.
Effective forWater characteristics
LimitationNot a health filter: Does NOT remove lead, arsenic, PFAS, chemicals, or bacteria
Point-of-Entry Whole-HouseAlso: Under-Sink Point-of-Use Stage
Ultraviolet (UV) Disinfection
- NSF/ANSI 55Ultraviolet Microbiological Water Treatment Systems, Class A / B
Water travels through a quartz sleeve surrounded by a germicidal UV-C lamp emitting light at 254 nanometers. The UV photon energy penetrates microbial cell walls and disrupts their DNA/RNA dimer bonds, preventing replication and infection.
Effective forMicrobes
LimitationDoes not remove any dissolved chemicals, heavy metals, minerals, or particulates
Whole-House Pre-FilterAlso: Under-Sink Stage 1
Mechanical Sediment Filtration
- NSF/ANSI 42Particulate Reduction, Class I–VI
Depth or pleated spun-polypropylene cartridges capture suspended solids through physical straining.
Effective forWater characteristics
LimitationDoes not remove dissolved chemicals, heavy metals, or microscopic dissolved ions