RO Maintenance & Troubleshooting: When to Replace RO System Cartridges & Sanitize Your RO System

The following information is of a generic nature the principles of which apply to practically all residential reverse osmosis systems: Filter cartridges should be changed at frequencies recommended by us (see individual RO system listings or replacement cartridge descriptions) or in the owners’ manual. RO systems should, at least in theory, also be sanitized at least once every year (Click here for info on an easy-to-use liquid drinking water system sanitizer). However, if your RO system is constantly used, you will normally need to simply rinse the housings (without detergent) before inserting new cartridges, and that every two to three months the RO storage tank should be emptied of most of the water contained (by leaving the counter top dispenser faucet on) until only a "thin" line of water comes out from the spout. If the RO system produces significantly less water than "normal" (when cartridges are new), that means one or more filter cartridges may be clogged and have to be changed. Better still, an inexpensive TDS (total dissolved solids) meter can be used to measure the rejection rate of the membrane: (TDS of feed water - TDS of product water)/TDS of feed water x 100%. The lower the rejection rate, the higher the need for filter cartridge or RO membrane change. The TDS meter measures the conductivity of dissolved and ionized substances (total dissolved solids) in water and, when converted by a factor, gives an indication in ppm (parts per million) of the average level of impurities in the water. Generally speaking, the higher the level of TDS in the water, the higher the electrical conductivity/ppm levels, and vice versa. A fully functional reverse osmosis membrane has a TDS rejection rate of 95% or higher. With the clogging up of pre-filters and lower feed water pressure, and the slow deterioration of the membrane over time, the TDS rejection rate will decrease, hence the quality of the product water will not be as good. Pre-filter cartridges: If this happens, the first thing to check for is clogging up of one or more of the pre-filters by sediments. If so, one or more of the pre-filters should be changed, and the TDS rejection rate will improve again (the TDS meter will show reduced ppm levels). To determine whether one or more of the sediment and carbon pre-filter cartridges are clogged up, turn off the water supply to the RO system, then disconnect the tubing leading from the out port of the last pre-filter housing of the series (unattach the tubing at the end where it goes into the 4-port automatic shutoff valve), then turning on the water to visually see how strong (or weak) the water flow is, which will give you an indication as to whether one or more of the pre-filter cartridges are clogged up. To check individual pre-filter cartridges for whether they are clogged up: 1) Turn off the water supply to the RO; 2) Remove all pre-filter cartridges from their housings, except cartridge #1; 3) Turn on the water supply, and check for strength of water flowing out from the centre orifice on the cap of the 2nd housing; 4) Turn off water supply, add cartridge #2 to its housing; 5) Turn on the water supply, and check for strength of water flowing out from the centre orifice on the cap of the 3rd housing; 6) Turn off water supply, add cartridge #3 to its housing; 7) UNATTACH the piece of tubing connecting the 3rd housing to the 4-port automatic shutoff valve at the distal end; 8) Turn on the water supply, and check for strength of water flowing out from the OUT port of the 3rd housing (make sure the end of the tubing from the OUT port of the housing is directed to a container to catch the water and not let it spill onto the floor). RO membrane: A TDS meter helps you determine whether the RO membrsne needs to be changed. If the pre-filters are working properly (no clogging up and/or have only recently been changed), compare the TDS level of the feed water and the product water from the RO system. The membrane is working well if the TDS level of the product water is significantly less than that of the feed water. If changing of pre-filters cannot improve the water production rate nor reduce the TDS level, the RO membrane will have to be changed. The life of the RO membrane in a properly maintained RO system is about 3 to 6 years or even longer. However, at what ppm level the RO membrane is to be changed is a subjective decision. A good rule of thumb is when the product water ppm is at a level of higher than 30% of the feed water's ppm level. For instance, if the feed water's ppm is 200, and the product water's ppm level is more than 60 even after the pre-filters have been changed, it is time to change the RO membrane. If you do not have a TDS meter, you should do the following to find out if the production rate of purified water is too slow. If the product water flow rate is too slow (and you are sure the flow through rate in the series of pre-filter cartridges is normal), then the RO membrane needs to be changed: (1) Turn off storage tank valve; (2) Turn on dispenser faucet; (3) Observe the purified water flow (with the storage tank valve turned off, what you see is the real RO water production rate by the RO membrane); (4) If the purified water is in a weak or strong stream, the RO membrane should still be good. If the water is only dripping out (fast or slow drip), the RO membrane needs changing. Storage tank pressure: Sometimes it may be the storage tank that has lost pressure. You can tell whether this is a problem by allowing the RO system to produce and store water for two hours without drawing any water for use, then turning off the feed water supply to the RO system and turning on the dispenser faucet, allowing the water in the storage tank to flow out. If the water flowing out is very little and no more than 4L/1gal, then it is very likely that the storage tank has lost part or all of its pressure. To fix this problem, use a suitable hand pump to increase the pressure of the tank. Pump no more than 5 to 10 times (depending on the capacity of the pump), then test the storage tank again). The tank's normal pressure is quite low: 5 to 10 psi being the normal range of pressure. OTHER USEFUL TIPS The following tips assume a basic 5-stage RO System in use and should be modified for other models as their designs may vary: (A) To determine the rate of water production of an RO system, follow these steps: 1. Turn off the water supply to the RO system; 2. Turn off the shutoff valve of the RO water storage tank; 3. Turn on the water supply to the RO system again; 4. Flip up (in locking position) the handle of the countertop dispenser faucet and observe trhe flow of water coming out from the spout, either as a fine stream or in drips; 4. After a minute or two when the flow pattern is stabilized, collect the water in a small cup for one minute; 5. Measure the volume of water using a suitable container with graduated volume measurements; 6. Convert the flow rate into gallons per day (1 U.S. gallon = 3.785L; 1oz = 30ml) 7. Calculate the corrected production rate of the RO membrane using this formula: Measured flow rate x Temperature Correction Factor (TCF)@feedwater temperature. The TCF-temperature chart is available at this Dow Chemicals link. Compare the Corrected Flow Rate (CFR) with the rating of the RO membrane – The RO membrane is considered good if the CFR is within 15% of the RO membrane rating, otherwise at least one filter cartridge may be clogged and needs changing. If all pre-filters are good, then the RO membrane will need to be changed. (B) To determine which pre-filter cartridge(s) needs changing, follow these steps: (Make sure your hands are clean) 1. Turn off the water supply; 2. Turn on the countertop dispenser faucet and let all stored water be drained; 3. Disconnect the RO membrane end of the tubing joining the last pre-filter housing to the RO membrane housing; 4. Unscrew the second pre-filter housing and take out the filter cartridge; 5. Place the cartridge on a clean plate to avoid accidental contamination; 6. Clean the housing using tap water (detergent is not necessary) and put it aside; 7. Put a container under the second housing cap to catch water, then turn on the water supply; 8. If the water drips or flows very slowly from the cap, that means the first pre-filter cartridge is clogged; 9. Unscrew the first housing and replace the filter cartridge; 10. Repeat these steps, if necessary, for all three pre-filter housings to determine whether each pre-filter is clogged; 11. Reconnect the tubing joining the last pre-filter housing to the RO membrane housing; 12. Follow Steps A1 to A7 to see whether the RO membrane is clogged and needs to be changed. (C) To sanitize an RO system, follow these steps: (To perform the procedure, you need to have an additional piece of tubing preferably at least 2 ft/0.7m long) 1. Turn off the water supply; 2. Turn on the countertop dispenser faucet and drain all water from the storage tank; 3. Unscrew all pre-filter housings, take out all the cartridges (Place any cartridge to be reused on a clean plate, and dispose of any cartridges not be to reused) 4. Clean the filter housings, if necessary, particularly if they are lined by sediments and/or biofilm growth (ordinary “clean” tap water can be used to clean the housings - do not use detergents); 5. Pour about 2.5 ml (half teaspoon) of normal unscented household bleach (5.25% sodium hypochlorite solution) into the first pre-filter housing; 6. Screw back all pre-filter housings; 7. Disconnect the tubing connecting the automatic shutoff valve and the tee connector at the tee connector end; 8. Disconnect the tubing at the out port of the last filter housing; 9. Use the extra piece of tubing to connect the out port of the last filter housing and the vacant port of the connector tee; 10. Disconnect the tubing joining the connector tee and the post-filter at the tee connector end; 11. Disconnect the tubing joining the dispenser faucet and the post-filter at the post-filter end; 12. Insert the free end of the dispenser faucet tubing to the vacant port of the connector tee; 13. Turn on the water supply and let water run out from the countertop dispenser faucet for about 10 seconds; 14. Turn off the countertop dispenser faucet (storage tank valve should be kept on); 15. Wait about 5 seconds then turn off the water supply; 16. Turn on the countertop dispenser faucet again to let water run out (only some residual water will run out); 17. Wait for about 1 hour to let the chlorinated water sanitize the RO system; 18. Unscrew and drain all housings, then re-insert filter cartridges into the housings; 19. Re-connect all the tubing according to their original configuration, 20. Turn on the water supply and wait for product water to flow out slowly from the countertop dispenser faucet which should be turned on at this stage; 21. Turn off the countertop dispenser faucet and wait about three hours (average) for the storage tank to fill completely; 22. Turn on the countertop water dispenser and drain all water from the storage tank until the product water slows down to a trickle. 23. Use a cup to catch some of the water: Either try to smell to ascertain whether there is any taste of chlorine in the water or use a chlorine test kit to ascertain that there is no chlorine in the product water; 24. If chlorine is detected, the post-filter needs to be changed. 25. If no chlorine is detected, repeat Step 21 and the RO system is ready for service. (D) To change the RO membrane, follow these steps: 1. Turn off the water supply, turn on the countertop dispenser faucet and drain all water from the storage tank; 2. Disconnect the tubing joining the last pre-filter housing to the RO membrane housing; 3. Unscrew the RO membrane housing cap; 4. Replace the RO membrane; 5. Screw the cap back on; 6. Re-connect the tubing; 7. At this stage, you may choose to replace the post-filter cartridge; 8. Turn on the water supply; 9. Follow procedure in Section (A) above to calculate the flow rate of the product water. (E) To accurately measure the TDS level of RO systems: Use a TDS meter. Please see our TDS meter listings for details and tips on using the TDS meters. (F) Some customers may observe carbon fines in the product water initially when a new RO system has been installed or when a new post-carbon filter is installed. This is completely normal as harmless carbon fines are produced in the manufacturing process. They will either go away within a few tankfuls of water are drained, or you can flush them away by disconnecting the carbon post-filter and then connecting the feed water tube to the in-port of the post-filter. Another option is to replace the carbon (GAC) post-filter by a carbon block post-filter (which does not release carbon fines but is somewhat more expensive) when you change the post-filter in the future. Note: For users who do not want to go through the above troubleshooting procedures, a simple rule of thumb for changing the cartridges for an RO system: - Cartridge #1 (Sediment pre-filter): 6-12 months (high-capacity washable pleated filters: 6-24 months); - Cartridge #2 (Pre-carbon): 6-24 months; - Cartridge #3 (RO membrane): 3-6 years; - Cartridge #4 (Post-carbon): 2-4 years. Revised: Sep 30, 2016