my express water ro system water tastes kinda bitter or metallic, did i install it wrong?

Diagnosis

This bitter or metallic taste in your Express Water RO5DX system is typically caused by one of two scenarios: "carbon fines" leaching into the water during the initial break-in period, or a failure in the final polishing stage. If the system is brand new, the activated carbon in the pre-filters and the final post-carbon filter can release microscopic particles (fines) that create a sharp, metallic tang. This is common if the system wasn't flushed thoroughly before the first drink. Alternatively, if the system has been running for several months, the post-carbon filter (the final horizontal stage before the faucet) has likely become saturated. Because the RO membrane removes almost all dissolved solids, the water becomes slightly acidic. The post-carbon filter is designed to balance this pH and strip away any residual tastes. When this filter fails, you taste the raw, stripped mineral profile of the RO water, which often manifests as a metallic or "bitter" flavor. To confirm, taste the water immediately after a long period of stagnation (overnight) versus after flushing the tank; if the taste is stronger after stagnation, the issue is likely the post-carbon filter or the storage tank bladder.

How to Fix It

To resolve the taste issues and ensure the system is operating at peak purity, follow these precise steps:

1. Isolate the Tank: Close the blue plastic valve on top of the pressurized storage tank. This ensures you are testing the water coming directly from the membrane and post-carbon filter, not the stored water.
2. Flush the Lines: Open the RO faucet and let the water run for 5-10 minutes. If the taste persists, the issue is with the filters.
3. Replace the Post-Carbon Filter: Locate the final horizontal filter cartridge (the "polishing" filter). Turn the locking mechanism or unscrew the housing depending on your specific RO5DX revision. Remove the old cartridge and install a fresh GAC (Granular Activated Carbon) post-filter. Ensure the O-rings are seated perfectly to prevent air leaks.
4. Refresh the Pre-Filters: If you haven't changed the three vertical canisters (Sediment, Carbon Block, and second Carbon Block) in 6 months, replace them now. Use a housing wrench to unscrew the canisters, rinse the inside of the housings with clean water, and install new 10-inch standard filters.
5. Sanitize the Tank: Open the tank valve and allow the system to fill completely. Once full, drain the entire tank through the faucet. Repeat this "fill-and-drain" cycle twice to purge any stagnant water or carbon fines trapped in the bladder.

If That Didn't Work

• Check the Membrane Seal: If the taste is intensely metallic, the RO membrane (the large center housing) may have a compromised seal, allowing "bypass" where raw tap water leaks around the membrane and mixes with the purified water. Remove the membrane and check the rubber gaskets for tears or misalignment.
• Inspect the Storage Tank Bladder: If the taste only occurs after the water has sat in the tank, the internal rubber bladder may be degrading. Tap the bottom of the tank; if it feels heavy but very little water comes out of the faucet, the bladder has failed and the tank must be replaced.
• Test Feed Water TDS: Use a TDS (Total Dissolved Solids) meter to check your tap water versus your RO water. If the RO water is higher than 10% of the tap water, the membrane is fouled and needs replacement regardless of the filter age.
• Verify Tubing Connections: Ensure no tubing is rubbing against the underside of the sink or against chemicals (like dish soap or bleach) stored under the counter. Plastic tubing can absorb odors and chemicals from the environment, which then leach into the water.

Heads Up

• Flush Schedule: If you do not use the RO faucet for more than 3 days, always run the water for 60 seconds before drinking to clear stagnant water from the lines.
• Filter Sequence: Always replace pre-filters every 6 months and the RO membrane every 24 months to prevent the membrane from "scaling" and affecting taste.
• Avoid Kinking: Ensure the 1/4" poly tubing has wide loops and no sharp kinks, as restricted flow can cause pressure pockets that affect the efficiency of the post-carbon filter.
• Leak Check: After replacing any filter, wipe all joints with a dry paper towel. Even a microscopic drip can lead to mold growth under the sink, which can affect the taste of the water via aerosol contamination.