RO
MEMBRANE REPLACEMENT
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RO MEMBRANE REPLACEMENT
How to tell if the RO membrane needs replacement:
The condition of the membrane is assessed by testing the percent TDS (Total
Dissolved Solids) rejection:
Using a TDS meter, compare the TDS of the inlet water to the pure RO water,
and obtain the percentage of TDS rejection.
Your supplier can help you to check your water quality, or you can purchase a
TDS tester to test by yourself.
% rejection rate = TDS of inlet water – TDS of pure water
TDS of inlet water
Example:
Inlet water TDS = 300ppm; Pure water TDS = 18ppm*
300 – 18
300
If rejection goes below 70% the membrane life has come to an end.
* After the RO membrane, the filtered water passes through the post filter which
adds minerals to the water, raising the TDS by about 10 -20 PPM. So the TDS
after the post filter will be higher than immediately after the RO membrane. As
long as the rejection rate calculated after the postfilter (final product water) is
above 70%, the RO membrane is still okay.
90 - 95% > Maximum Quality
70 - 80% > Low Quality
80 - 90% > Medium Quality
x 100
x 100 = 96% rejection rate
TDS Tester
