If you’ve decided you want certifiably “pure” water, you have multiple options. You can get a water service, delivering filtered water in bottles to your fridge or in 5-gallon carboys to a dispenser. You can get a whole-house or—in industry terms—point-of-entry filtration system, but these are mostly aimed at people with exceptionally hard (aka, mineral-rich) water. You can get a pitcher filter (we have tested them and have recommendations), or a countertop unit. You may also be able to install a filter in your fridge’s dispenser. Or you can get an under-sink (“point-of-use”) system.

Pitchers and under-sink filters both work the same way: Water flows through a canister containing activated charcoal and, often, an ion-exchange mechanism made of a specialized resin. The charcoal removes organic compounds, like pesticides, and particulate matter; the ion-exchange resin removes dissolved metals, with lead being the one most people are concerned about. (For details on how they work, see our filter-pitcher guide.) The other main class of under-sink filters, reverse osmosis, is not this guide’s focus—here’s why.

Both types are highly effective, but an under-sink system has a few advantages:

Convenience: You can get filtered water instantly just by turning on a faucet, versus having to wait for a pitcher to do its work. That includes saving the time it takes to to open the fridge, fill the pitcher, heave it out of the sink, and put it back in.

Capacity and speed: The highest-capacity under-sink filters can clean 1,000 gallons of water or more; most pitcher filters are rated to just 40 gallons. That means some under-sink filters can go for a year between replacement, whereas a thirsty family of four might need to replace a pitcher filter once a month. (The difference comes down to water pressure. A pitcher filter relies on gravity to draw water through the filter, and that means the charcoal filter has to be composed of loose beads or pellets—otherwise you’d wait all day for a drink. Under-sink filters, by contrast, push relatively high water pressure through a solid block of charcoal, which uses increased surface area and finer perforations to greatly boost the filtration capacity.)

Functionality: Almost anyone can operate a faucet; pitchers can be too heavy and unwieldy for kids and people with arthritis or difficulty with lifting.

Under-sink filters also have some disadvantages:

Size: Under-sink filters take up valuable storage space under the sink. It may not be much—our pick is about the size of a wine bottle, and it’s suspended under the sink, off the cabinet bottom—but it’s a consideration.

Installation: If you’re reasonably handy and have a sink that’s ready to accept an additional faucet—it’ll have an extra hole besides the main faucet, where a soap dispenser (for example) can be put in—you should be able to install an under-sink filter yourself. If not, you’ll probably need to hire a plumber. (Once the filter is plumbed in, you’ll be able to replace filters yourself—most, including our pick, have a simple twist-on-twist-off design.)

Temperature: Water from an under-sink filter is not as cold as water poured from a refrigerated pitcher, or filtered water from a refrigerator’s dispenser.

After 30 hours of reporting and research, we believe the MultiPure Aquaperform Under Sink Water Filtration System  is the best under-sink water filter for most people. Of the hundreds of filters we compared, few can remove as many contaminants.

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