SpectraPure
®
SpectraPure
®
Inc.
480.894.5437 Call us toll-free 1.800.685.2783
2167 East Fifth St, Tempe, Arizona 85281
20
TESTING THE QUALITY OF THE MEMBRANE:
The performance of a reverse osmosis membrane is measured by its
ability to reject salts or TDS (Total Dissolved Solids). It is expressed as the
percentage of the feedwater TDS that has been removed in the permeate
(product) water. This is referred to as Percent Rejection.
NOTE: All water sources are different and are subject to changes in
conductivity from season to season which could affect the TDS
reading depending on the time of the year. We recommend that
you test the quality of the membrane once every 6 months.
General Procedure:
1. Set Meter #1 (left side meter) to the “IN” position to measure the tap
water TDS. (Call it X)
2. Run the system for 15 -20 minutes.
3. Set Meter #1 to the “OUT” position to measure the TDS of the permeate
(RO) water. (Call it Y).
4. Subtract RO water TDS from tap water TDS. (X - Y)
5. Divide this quantity by tap water TDS. (X - Y) ÷ X
6. Rejection = [(X - Y) ÷ X ] ×100
Rejection of the RO Membrane Calculation Example
7. Tap water TDS = 150 ppm (X)
8. RO water TDS = 15 ppm (Y)
9. X - Y = 135 ppm
10. (X - Y) ÷ X = 135 ÷ 150 = 0.90
11. Rejection = [ ( X - Y) ÷ X ] ×100 = 0.90 ×100 = 90%
NOTE: Rejection rates less than 95% may indicate that the membrane
should be replaced.
TDS Meter set to the “IN” position.
Slide the switch to the right for
the “OUT” position.
