A purifier removes unwanted contaminants from air, water, or other substances to make them cleaner and safer. The specific contaminants depend on the type of purifier: air purifiers target dust, allergens, smoke, and chemical fumes, while water purifiers remove bacteria, heavy metals, and industrial chemicals. Beyond household use, purifiers also play critical roles in hospitals, factories, and maritime operations.
What Air Purifiers Remove
Air purifiers clean indoor air of two broad categories of pollutants: particles and gases. Particulate matter includes dust, pollen, pet dander, mold spores, bacteria, viruses, and smoke from cooking or tobacco. Gaseous pollutants come from combustion sources like gas stoves and vehicle exhaust, as well as from building materials, paints, adhesives, cleaning products, and pesticides. These gases often fall under the umbrella of volatile organic compounds, or VOCs, the chemical fumes released by everyday household products.
Different air purifier technologies handle different pollutants. Mechanical filters physically trap particles as air passes through them. Gas-phase filters use materials like activated carbon to grab gas molecules and hold them on the filter’s surface through a process called adsorption. UV-based cleaners destroy biological contaminants like bacteria and viruses using ultraviolet light rather than trapping them.
How HEPA Filters Work
The most common air purifier technology for home use is the HEPA filter. A true HEPA filter captures at least 99.97% of airborne particles down to 0.3 microns in size, which is roughly 300 times smaller than the width of a human hair. That 0.3-micron threshold isn’t arbitrary. It represents the particle size that’s hardest for the filter to catch, so anything larger or smaller is actually captured even more efficiently.
HEPA filters are effective against dust, pollen, mold spores, pet dander, and many bacteria. They do not, however, remove gases, odors, or chemical fumes. That’s why many home air purifiers combine a HEPA filter with an activated carbon layer: the HEPA catches particles, and the carbon handles smells and VOCs.
Choosing an Air Purifier by CADR
When shopping for an air purifier, the most useful performance number is the Clean Air Delivery Rate, or CADR. This metric tells you the volume of filtered air the unit delivers per minute, with separate scores for three pollutant types: tobacco smoke, pollen, and dust. A higher CADR means the unit cleans air faster. Matching the CADR to your room size is the simplest way to make sure a purifier can actually handle the space you’re putting it in.
What Water Purifiers Remove
Water purifiers target a different set of threats: bacteria, viruses, parasites, heavy metals like lead, and chemical contaminants including PFAS (sometimes called “forever chemicals” because they persist in the environment for decades). Three main technologies dominate the home water purifier market, each with different strengths.
Carbon filters work by adsorbing impurities onto the surface of activated carbon as water flows through. They’re effective at improving taste and removing chlorine, some pesticides, and certain VOCs. NSF/ANSI Standard 42 certifies filters for these “aesthetic” improvements like taste and odor, while NSF/ANSI Standard 53 certifies filters that reduce health-related contaminants like lead and cryptosporidium.
Reverse osmosis systems push water through membranes with pores so small they block contaminants down to individual ions. This makes them the most thorough home filtration option, capable of removing heavy metals, dissolved salts, and many chemical pollutants that carbon alone would miss.
UV sterilizers kill bacteria, viruses, and parasites using ultraviolet light. They don’t remove chemicals or metals, so they’re typically paired with another filtration method for comprehensive treatment.
Removing PFAS From Drinking Water
PFAS contamination has become a growing concern, and the EPA identifies three filter types that can reduce these chemicals in home drinking water: granular activated carbon filters, reverse osmosis systems, and ion exchange resins (tiny beads that attract and hold contaminants as water passes through). If you’re buying a filter specifically for PFAS, look for certification to NSF/ANSI 53 or NSF/ANSI 58 for PFAS reduction on the packaging. As of April 2024, filter certifications focus on removing PFOA and PFOS, the two most studied types of PFAS.
Hospital and Medical Uses
Purifiers aren’t just household gadgets. In hospitals, HEPA and UV-based air cleaners serve a much higher-stakes role: preventing the spread of airborne infections like tuberculosis, chickenpox, and measles. One common application is creating negative-pressure isolation rooms, where an air cleaner exhausts air out of the room to prevent infectious particles from escaping into hallways. Emergency departments and isolation rooms are the most common locations for these units.
Surgical suites and clean rooms use filters rated at the highest efficiency levels (MERV 17 through 20) to remove even viruses from the air. UV systems are also used inside ventilation ducts in high-risk areas like autopsy suites and rooms where patients with undiagnosed tuberculosis might be examined.
Industrial Purifiers
Outside of air and water, purifiers are essential in heavy industry for cleaning oils and fuels. Hydraulic oil purifiers, transformer oil purifiers, and turbine oil purifiers all remove water and solid contaminants from the fluids that keep machinery running. In maritime operations and power plants, fuel oil purifiers clean fuel before it reaches engines or turbines. Removing these contaminants extends the life of expensive equipment, reduces maintenance costs, and prevents breakdowns that could shut down operations.