What the best water filter has

  • A large enough capacity. Pitcher water filters are very affordable and easy to use, but their capacity is so limited that they're best for just keeping a supply of drinking water on hand. Countertop, faucet-mounted and under-sink water filters give you an unlimited amount of filtered water, and have the added convenience of letting you toggle between filtered and tap water.
  • The proper filtering mechanism. Most water filters use carbon, which absorbs impurities and odor as the water passes through the porous material. Multistage filters can remove contaminants such as lead, chlorine, parasites, pharmaceuticals, bacteria and harmful chemicals, and the semi-permeable membranes of reverse osmosis systems flush the highest percentage of contaminants away.
  • A moderate to fast flow rate. Most water filters will noticeably slow your flow rate, but a unit becomes inconvenient if it takes too long to do its job. Flow speed varies depending on the type of water filter. Some water filters also slow down as the filter gets toward the end of its useful life; a filter change should fix that.
  • Certifications backing up contaminant removal claims. Manufacturers may test their own products, but a water filter isn't certified to remove contaminants unless it has been tested by an independent organization like NSF Internationalor the Water Quality Association. Both have databases that consumers can easily search to learn more about the reliability of specific models.
  • A filter change indicator. Water filters that measures how much water you have used and then alert you with a light is the most accurate way to determine if your filter needs to be replaced. Other units may include timers or stickers to count remind you after a certain period of time, usually 3 to 6 months.
  • Compatible attachments. For installed filters, the best systems are compatible with a wide range of faucets, sinks and plumbing. Occasionally, consumers may need to purchase additional connections or accessories like extension hoses or icemaker hookups to make a filter more usable. Some water filters have faucets available in a variety of finishes to match your existing dĂ©cor.
  • Long warranty. A 90-day warranty may be suitable for a pitcher filter, but a longer warranty of one or two years is best for any filter that requires installation.

Know before you go

What contaminants affect your drinking water? Not all water is the same, and it's important to know what contaminants are present in the drinking water in your area. This will help you determine whether you need only a basic filter to improve taste or a sophisticated system that reduces pollutants and parasites. More information on your local water supply and how to find a state-certified tester can be found at the United States Environmental Protection Agency website. Once you pinpoint your specific water concerns, you can identify the best water filters for your needs.

How much water do you want to filter? If problems like sediment or sulfur are severe, you may want to consider a whole-house filter, although these won't remove all contaminants. If you need filtered water just for drinking, a pitcher may suffice. Cooks will find faucet-mount and under-sink filters more convenient as they won't need to continuously refill a carafe. Hard water won't be helped by a filter at all, for that you need a water softener.

How permanent do you want the water filter to be? Pitcher or faucet-mounted water filters are likely the best option for dorm residents or renters who can't make permanent modifications to their living spaces. Under-sink water filters are permanent and may require you to drill a hole for the filter faucet. These may require a certain level of expertise to install, which could necessitate hiring a plumbing professional.

Value expectations: the dollars and cents of it

Consider annual cost and maintenance requirements. Water-filtering pitchers and faucet-mounted filters aren't that expensive, but the cost of replacement filters will quickly outpace the initial purchase price. Use the cost of replacement filters and manufacturer recommendations on filter life to estimate your annual expenses. Cleaning, battery replacement and new semi-permeable membranes are additional charges for reverse osmosis systems. Also, consider the cost of discarded waste water if your supply is limited or you have high municipal water rates.

Elsewhere in this report:

Best-reviewed water filters: Whether you just want better tasting drinking water, or need to purify your entire water supply, these are the best water filters for improving water clarity, taste and safety.

Best water filter pitchers: A water filter pitcher gives you a supply of cold, filtered water in your fridge at all times. They come in a wide range of sizes and are affordable and easy to use.

Best faucet water filters: Countertop and faucet-mounted water filters give you unlimited amounts of filtered water without a permanent installation; these are the best, easiest to install faucet water filters.

Best under-sink water filters: Water filters that install under the sink filter out more contaminants and particulates than most other types of filters; reverse osmosis filters are even more purifying.

Best whole house water treatments: If you need to treat your water problems at the source, whole house water treatment systems are the best choice. We discuss both water filters and water softeners.

Our Sources: These are the expert and user reviews and recommendations we used to find the best water filters. They are ranked in order of credibility and usefulness.

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