Easy TDS Membrane Performance Calculator

See If It is Time To Replace Your Membrane

Feed Water TDS

RO Water TDS

Submit

Simply enter your Feed Water TDS and RO Water TDS into the boxes above and click "Submit". The percentage of TDS Rejection will be displayed. We normally recommend membrane replacement once you drop below 75%. This may vary in areas with high TDS in the feed water.

See our selection of TDS meters under Water Tests

Be sure to check our Parts Department for important replacement parts for your Water Doctors Replacement Filter PRO-2000, SMP-3000 & PRO-4000 Reverse Osmosis System such as TDS Testers For Reverse Osmosis Membranes, Replacement Tanks, O-rings, Faucets, Pumps, Fittings, UV Systems and more service parts for your reverse osmosis pure water filter system.   View maintenance and servicing tips for Water Drs drinking water filter system online at our Installation & Trouble Shooting Guide. Water Doctor replacement filters.

* Water Doctors ® is the registered trademark of HMI Water Specialists, Minneapolis, MN USA, the manufacturer of Water Drs brand drinking water filtration equipment.  The replacement water filters and reverse osmosis membranes listed above are not manufactured or endorsed by HMI Water Specialists.  Rather, these replacement filters and RO membranes are manufactured by other companies.  While these repalcement filters and membranes are compatible for use in Water Doctors SMP-3000, PRO-2000 & PRO-4000 reverse osmosis water filtration equipment, we make no representation as to whether using these repalcement water filters and RO membranes is consistent with the warranty and specifications applicable to Water Doctors water filter equipment.