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.
3. Calculate Percent Rejection:
Use the following formula: 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. Example:
| Tap TDS = 260 ppm || RO TDS = 20 ppm || Rejection = [(260 - 20) / 260] x 100 |
| || || = [240/260] x 100 |
| || || ≈ (.923) x 100 |
| || || = 92.3% |