Undersink Water Filters

These water filters require plumbing installation but fewer filter changes

Under-sink water filters require installation, so you need either plumbing expertise or a professional. You may also need an extra hole in the sink to accommodate an extra faucet just for filtered water. Under-sink filters don't usually need changing as often, though, compared with water filters that don't require installation.

Regular carbon-filter under-sink models are adequate for most users. We found the most recommendations for the Culligan brand, both for filtering effectiveness and for easy owner-installation. The current Culligan US-EZ-4 (*Est. $80) gets near perfect ratings from the half-dozen owners reviewing it at Amazon.com at the time of our report, partly because they find it very easy to install. The filter usually lasts six months or for 500 gallons, and the faucet includes an electronic indicator to monitor filter status. If you only want to filter out chlorine, Culligan also makes less expensive models such as the CUL SY-750S (*est. $45), which installs in a similar way.

The Kenmore Single Undersink 38454 (*est. $50) receives good ratings in comparison tests, but it has drawn criticism from several owners at Sears.com for a fragile plastic dispenser head and a plastic cartridge holder that can break and leak. Comparison tests also give the dual-stage Sears Kenmore 38460, now the 38461 (*est. $85), good ratings for filtering effectiveness but lower ratings for flow rate. We found only five owner-written reviews of this model at Sears, all fairly recent, and none of them complain about the flow rate.

Reverse osmosis water filters

The most powerful under-sink water filters use reverse osmosis. Experts recommend this type only if your water has extra contaminants such as nitrates, since reverse-osmosis filters waste water as they work. Some waste as much as 5 gallons of water for every gallon of filtered water produced. This filtering process is also much slower than most, and they filter out "good" minerals your body may need.

Comparison tests give the Whirlpool WHER25 (*Est. $195) sold at Lowe's good ratings for effective filtering, and it's also one of the top-rated water filters rated by more than 100 owners there. Neither the manufacturer nor the reviews specify how much water this model uses. Owners do mention that you're locked into buying proprietary Whirlpool filters -- easier to replace than some, but more expensive.

Comparison tests also give the Kenmore 38556 (*est. $255) similar ratings for effectiveness and flow rate, and this reverse-osmosis filter gets good reviews from owners at Sears.com. It's NSF-certified to filter out 13 contaminants, including nitrates, cysts and various heavy metals. We found no mention of MTBE (filtered by the Whirlpool WHER25) or other more exotic pollutants.

Both the Whirlpool and Kenmore models require storage tanks under the sink. The reverse-osmosis filter recommended by staff at the Allergy Buyers Club, the Blueair BL WP RO3 (*est. $3,000), is a direct-flow model that doesn't need a storage tank, so it takes less space. Even though it's considered one of the most efficient reverse-osmosis water filters available, it still wastes almost half a gallon of water for every gallon that's purified. This is one reason why experts recommend resorting to this type of water filter only if you really need the extra protection.