Under-Sink Water Filters

Under-sink water filters require plumbing installation but fewer filter changes

Under-sink water filters are another way to make greater quantities of filtered water readily available. The filter is hidden out of view and doesn't encroach on sink workspace like faucet-mounted filters do. Plus, the filters last months longer than pitcher and faucet-mounted types. However, a separate faucet must be installed and the plumbing modified, which requires expertise or a professional.

Under-sink water filters can differ in price by hundreds of dollars. If you are looking for a balance of price and filter capability, one consumer testing organization recommends the Whirlpool Dual Filtration System WHED20 (*Est. $100), Omni CBF-3 (*Est. $110) and Culligan Preferred 350 (*Est. $155). Under-sink water filters aren't widely sold online, and we found a very limited number of reviews at sites like Lowes.com and Sears.com. You may have to purchase a filter directly from the manufacturer or a local plumber, who may also offer advice about which model to choose.

Reverse osmosis water filters have special filtering capabilities

Reverse osmosis water filters have the same pros and cons as under-sink carbon filters, but they add the filtering capability of a semipermeable membrane. If you have private well water, a reverse osmosis water filter may be necessary to remove sediment and potentially harmful arsenic, metals, minerals and contaminants that carbon cannot filter. A reverse osmosis system has a three-part filter and a storage tank. Water flows through a carbon pre-filter to remove sediment, particulate matter and chlorine. Next, it flows though a semipermeable membrane, where contaminants are trapped and flushed down the drain. The filtered water flows into a storage tank and then through a carbon post-filter to improve taste and odor when the faucet is activated.  If you don't have space under the sink, some systems allow the filters and multigallon storage tank to be installed in the basement or another more remote location.

In addition to the higher cost of a reverse osmosis water filter, its more invasive kitchen installation may require that an individual to have some plumbing knowledge or to hire a professional. There are a few other drawbacks to a reverse osmosis water filter worth noting. According to TheGreenGuide.com, this type of filter "wastes 4-9 gallons of water for every gallon filtered" because a stream of water must continually flush contaminants from the membrane during filtering. In addition, it also filters water very slowly.

One comparison test of four reverse osmosis water filters identifies the Whirlpool Reverse Osmosis Filtration System WHER25 (*Est. $150) as a good moderately priced choice; it's as good or better at filtering and removing bad taste as more expensive models. This system is NSF-certified to remove 14 contaminants, including chlorine, arsenic and nitrate. Its two carbon filters are sold in a pack for $35 and need replacing only every six months. The membrane costs nearly twice as much, but lasts a year or longer. According to the manufacturer, 5 gallons are wasted to filter a single gallon of water using this system. At Lowes.com, where the WHER25 water filter is sold, about 30 owners have posted reviews. Reviewers are enthusiastic about the quality of the filtered water and praise the water filter-change indicator light. A few owners say they were disappointed to find out the system doesn't work with extremely hard water.

The Kenmore Elite Premiere Reverse Osmosis Drinking Water System 38556 (*Est. $255) costs considerably more, but it also earns favorable ratings in one professional review. Like the Whirlpool reverse-osmosis filter, it is NSF-certified to improve taste and odor as well as remove turbidity (fine particles) and 13 other contaminants, including arsenic and nitrate. A few benefits this higher-priced RO system offers are an electronic filter-change indicator light that gauges usage, while the Whirlpool indicator merely flashes after six months have passed. Also, the filter housing doesn't need to be mounted under the sink, and kitchen items can be stacked on top of it without losing storage space. A 2-pack of carbon filters costs about $10 more than the Whirlpool's filters, but the reverse osmosis membrane is $10 less. About 20 owner reviews at Sears.com say the water quality is good and it's easy to install. A few dissatisfied customers say the filter indicator light was faulty, or they couldn't find replacement reverse osmosis membranes online and had to call Sears.