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How to Install a Water Conditioner

Ask This Old House plumbing and heating expert Richard Trethewey installs a water conditioner to combat hard water


  1. Before doing any work on the plumbing system, ensure that water is turned off at the main shutoff.
  2. Locate an area on the wall near the water main where the citric-acid conditioner can be installed. Ensure the location has enough clearance for the filters to be easily changed.
  3. Locate studs in the wall and mount a piece of scrap wood to the structure to serve as a backer for the conditioner using a drill driver and screws.
  4. Assemble the citric-acid conditioner using the instructions with the kit. Screw the mounting brackets to the heads of the filter, then attach the unit into the plywood backer board on the wall.
  5. Measure, cut, and dry fit the pipes to connect the main water line to the conditioner. Cut the pipes with the pipe cutter and clean the ends with sandpaper before dry fitting.
  6. Disassemble the pieces, apply flux to the pipe and fittings, and then solder the connections.
  7. Install the cartridges to the filter. The carbon filter should be installed immediately downstream from the main water shutoff, and the citric-acid conditioner should be installed downstream from that. The kit comes with a wrench that can tighten the cartridge to the filter.
  8. Turn the water back on and check for leaks.