Home How To Measure TDS
How To Measure Percent Rejection with a TDS Meter:

Follow These 3 Easy Steps:
Note: The following steps require a TDS Meter.
  1. Feed Water TDS: Measure the TDS of your raw feed water by submersing the tester's probes into a cup or glass of TAP water. Record the results.
  2. RO Water TDS: Measure the TDS of your RO Water by filling a cup or glass with RO water (from RO faucet) and submersing the tester's probes into the water. Record the results.
    NOTE: If the system is new or the membrane has been replaced, do not test the first tank of RO water. The first tank of product water will contain sanitizer and possibly carbon fines from your new filters. This will cause false reading.
  3. Calculate Percent Rejection: Use the following formula

     

    Example:
    Tap TDS = 260 ppm
    RO TDS = 20 ppm
    Rejection = [(260 - 20) / 260] x 100
    = [240/260] x 100
    ≈(.923) x 100
    = 92.3%

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