Overview

water filter
Illustration: Gregory Nemec
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Americans spend nearly $6 billion a year on bottled water, and the rest of the world chugs down another $29 billion worth of the stuff. Given this trend, we asked This Old House plumbing and heating expert Richard Trethewey to show us how to install an undersink water-filtration system.

Richard chose a dual-cartridge water filter for this kitchen. This model has both carbon-block and granular-carbon filters, as well as a dedicated faucet and an electronic monitor that signals when it's time to replace the filters (after 500 gallons have passed through them, or six months). Dual filters reduce most common chemicals and contaminants found in tap water—from a municipal source or ground well—including lead, mercury, asbestos, pesticides, and cysts. They'll also eliminate sediment, and bad taste and odors caused by the chlorine added to municipal water supplies.

The system shown here comes with all the necessary hardware and tubing to complete the installation. However, Richard upgraded the system by adding a new ball valve to the water-supply tubing that feeds the filters. This allows the homeowners to shut off the water to the unit to change the filter without cutting off the sink's main faucet.
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    Tools List

    • drill
      Drill/driver with step-drill bit,
      to drill hole in sink top
    • propane torch
      Propane torch
    • emery cloth
      Emery cloth,
      for cleaning pipe prior to soldering
    • adjustable wrench
      Adjustable wrench
    • tongue-and-groove pliers
      Tongue-and-groove pliers
    • tubing cutter
      Close-quarters tubing cutter
    • basin wrench
      Basin wrench,
      to tighten hex nut that holds filter faucet to sink top
    • copper fitting brush
      Copper fitting brush (for cleaning copper tubing and fittings
    • 16-foot tape measure
      Tape measure
    • eye goggles
      Eye goggles
    • centering punch
      Center punch,
      to strike a starting point on stainless steel sink deck prior to drilling

    Shopping List

    1. WATER FILTER KIT

    2. LEAD-FREE SOLDER AND PIPE FLUX

    3. 1/2-INCH COPPER TEE

    4. SEVERAL FEET OF 1/2-INCH COPPER TUBING

    5. 1/2-INCH FEMALE ADAPTER

    6. 1/2-INCH TO 1/4-INCH REDUCER

    7. 1/2-INCH BALL VALVE

    8. TEFLON TAPE

    applied to reducer before threading onto female adapter



    9. TARP OR BLANKET

    to protect kitchen floor



    10. FIRE-RESISTANT CLOTH AND FIRE EXTINGUISHER