Water filter types compared
There are six common designs. They differ in what they can reduce, how much water they handle, and how much upkeep they need. Start with what's in your water, then pick the smallest system that is certified for it.
| Type | Best for | Certifications to check | Cost |
|---|---|---|---|
| Pitchers and dispensers | Better taste, renters, small households, and some lead or PFAS reduction depending on the cartridge. | NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 401 | Low upfront, cartridges add up |
| Faucet-mount filters | Filtered water on demand without plumbing work. | NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 401 | Low |
| Under-sink carbon systems | Households that drink a lot of tap water and want more capacity with less upkeep. | NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 401 | Medium |
| Reverse osmosis (RO) | The broadest reduction, including PFAS, nitrate, arsenic and dissolved solids. | NSF/ANSI 58 NSF/ANSI 42 NSF/ANSI 53 | Medium to high |
| Countertop and gravity systems | Renters who want more capacity than a pitcher, or households preparing for emergencies. | NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 58 | Low to high |
| Whole-house (point of entry) | Chlorine taste in showers, sediment, hardness, and well water treatment. | NSF/ANSI 42 NSF/ANSI 44 NSF/ANSI 55 | High |
Pitchers and dispensers
Water drips through a cartridge, usually activated carbon, sometimes with ion-exchange resin. Performance depends on the cartridge, not the pitcher. Two cartridges that fit the same pitcher can carry very different certifications, so check the exact cartridge model. They are slow and small, and cartridges need replacing every few weeks to few months.
Check for: NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 401
Faucet-mount filters
A carbon block clips to the faucet with a diverter. They do not fit pull-down or some designer faucets. Flow is slower than the open tap, and hot water should never run through them.
Check for: NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 401
Under-sink carbon systems
One to three cartridges under the sink feed either the main faucet or a dedicated tap. Larger carbon blocks give more contact time than pitchers, and cartridges last months rather than weeks. Many models carry broad NSF/ANSI 53 claims, but you still need to check the listing for your contaminant.
Check for: NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 401
Reverse osmosis (RO)
Water is pushed through a semi-permeable membrane, usually with carbon pre- and post-filters and a storage tank. In the Duke and NC State study of home filters, under-sink RO units removed 94% or more of the PFAS tested. Trade-offs: some water goes to the drain, installation is more involved, and the membrane also removes minerals like calcium and magnesium.
Check for: NSF/ANSI 58 NSF/ANSI 42 NSF/ANSI 53
Countertop and gravity systems
This category ranges from large gravity dispensers to countertop RO units. Certification varies more here than anywhere else. Some popular gravity systems publish their own lab reports instead of independent certification, so read the fine print.
Check for: NSF/ANSI 42 NSF/ANSI 53 NSF/ANSI 58
Whole-house (point of entry)
Treats all water entering the home. Good for chlorine, sediment and scale (with a softener certified to NSF/ANSI 44) and, for wells, UV disinfection certified to NSF/ANSI 55. Not the right first tool for PFAS: in the Duke and NC State study, PFAS levels rose after filtration in 4 of 6 whole-house carbon systems tested, and removing chlorine can let bacteria grow in home pipes. Pair it with a point-of-use filter at the kitchen tap if drinking water is the concern.
Check for: NSF/ANSI 42 NSF/ANSI 44 NSF/ANSI 55
A certification number alone is not enough. NSF/ANSI 53 covers dozens of contaminants, and each product is certified only for the ones listed on its performance data sheet. See NSF certifications explained for how to check a model in two minutes.