Reverse Osmosis System Problems: Slow Flow, Taste and Leaks, and What to Check First

When a reverse osmosis system starts acting up, the cause is almost always one of a short list of usual suspects: feed pressure, a spent cartridge, a tired membrane, a fitting that isn't fully seated, or a valve that has stopped sealing. The fastest way to find out which one you're dealing with is to work through the checks in order of cost and effort, starting with the information your system may already be showing you, before you open anything up or start swapping parts on a guess.

• Read the display and lights first. A smart TDS reading and per-cartridge filter-life indicators, where a system has them, already tell you a lot before you touch a single fitting.
• Start cheap and easy, then go deeper. Feed pressure, temperature and an obviously lit warning cost nothing to check; the membrane is the last thing to suspect, not the first.
• A slow faucet with a slow drain line usually points to a clogged prefilter; a slow faucet with a normal drain line usually points to the membrane.
• A steadily climbing TDS number over several weeks, separate from any pressure change, is the typical sign of a membrane nearing the end of its working life.
• Most housing leaks trace back to a worn O-ring or tubing that isn't pushed fully home, not a cracked part.

Start Here: A Quick Way to Narrow Down What's Wrong

Before assuming the worst, separate the checks that cost nothing from the ones that involve a wrench. A system with a smart display and filter-life lights, such as the Hydrion Purity RO600, is already reporting part of the diagnosis: a live TDS reading at the faucet, and a light on each of its three cartridges that flashes red once that stage has under 5% of its rated life left. That information costs nothing to read and rules out or confirms several possibilities immediately.

From there, work outward. Feed pressure and water temperature are the cheapest things to verify, since they affect nearly every symptom here and need no tools. A loose fitting or an indicator light that's already lit comes next. The membrane, which sits furthest inside the unit, is the last thing to suspect rather than the first. Each section below follows that order, and links out to a more detailed article where the fix itself, rather than the diagnosis, needs its own space.

Slow or Weak Water Flow

Check Feed Pressure and Temperature First

Home RO systems are generally designed around a feed pressure of roughly 40 to 60 psi, and output drops measurably as the incoming water gets colder, by something like 1 to 2% for every degree Fahrenheit below about 77°F (source: Common Reverse Osmosis System Problems and Fixes). If your cold-water line runs noticeably below that temperature in winter, or if your home's pressure sits at the low end of that range to begin with, a slow faucet may simply reflect those conditions rather than a failing part. It's worth checking before replacing anything.

When the Cause Is the Membrane, Not the Filter

Once pressure and temperature are ruled out, a practical way to localize the problem is to compare two numbers: how much water comes out of the faucet over about 60 seconds, and how much goes to the drain line over about 30 seconds (source: Troubleshooting for Reverse Osmosis Systems). If both readings come back low, the sediment or carbon prefilter is the more likely culprit, since a clogged prefilter restricts the whole system before the water even reaches the membrane. If the drain flow looks normal but the faucet is barely producing anything, the membrane itself has probably scaled or fouled, since that pattern means water is reaching the membrane but isn't passing through it efficiently. Estimates for membrane life vary noticeably by source, from roughly 2 to 3 years in typical use up to a recommendation some guides make of replacing filters and the membrane twice a year as routine preventive maintenance, regardless of symptoms (source: Viomi Hydration Lab; source: NU Aqua Troubleshooting Guide), which is a reminder that water quality, not a fixed interval, drives the real answer. The RO600's own stated schedule is more specific to its cartridges: PPC sediment and carbon around every 6 months, the TC post filter around every 12, and the 600G membrane around every 24, per its product page, so treat that as this unit's own instruction rather than a universal rule.

Water That Tastes or Smells Off

An off taste or smell usually comes down to one of three things, and telling them apart matters because only one is a simple cartridge swap. Carbon media loses its ability to handle chlorine taste and odor as it ages, which is the most common and easiest cause to fix. Biofilm or bacterial growth in the lines or storage tank is less common, produces a similar musty taste, and usually needs a full sanitizing of the lines rather than a new filter. Dissolved gases such as hydrogen sulfide in the source water are the trickiest case: as a small, uncharged gas, it passes through an RO membrane largely unaffected, and clearing it usually calls for sulfur-specific treatment media, sometimes paired with carbon, rather than relying on the system's own stock carbon stage (source: Viomi Hydration Lab). A new carbon cartridge that doesn't resolve a persistent "rotten egg" smell points to the raw water itself, with the fix sitting upstream of the RO system rather than inside it.

Cloudy, Foamy or Discolored Water

Cloudiness right after installing a system or replacing its filters is usually trapped air or residual preservative from the new cartridges, and running the faucet, or fully draining a storage tank, a couple of times is commonly advised to clear it (source: Fresh Water Systems): a normal part of settling in a new cartridge, not a sign of a fault. Cloudiness that shows up weeks or months into otherwise normal use, and doesn't clear after running the tap, points back to the same filter or membrane condition covered above, so work through those checks rather than treating it as its own separate problem.

The System Won't Stop Running to the Drain

On a conventional tank-based RO system, filtered water builds up in a pressurized storage tank, and as that tank fills, backpressure against the incoming line is what should trigger a shut-off valve and stop flow to the drain. Full-tank shut-off pressure is generally expected to land around two-thirds of incoming line pressure, so continuous draining once the tank should be full usually traces to a worn flow restrictor or a check valve that has stopped sealing (source: NU Aqua Troubleshooting Guide).

A tankless unit like the RO600 works differently, since it has no storage tank and supplies water on demand through its own booster pump. Its membrane flushes automatically for a short period after power-on, after longer stretches of use, and roughly once every 24 hours on standby, and the unit pauses itself after 30 minutes of continuous running as a built-in safety stop, per its product page, so drain flow that follows that pattern is expected rather than a fault. Water going to drain well outside those windows, or a 30-minute pause that doesn't seem to engage, is worth a quick check that the faucet valve is fully closed; past that, the pump and valve logic sit sealed inside the unit, so support is the next step rather than opening it up further.

A Rising TDS Number on the Display

A smart TDS display turns a membrane's slow decline into a number you can actually watch over time. Higher incoming TDS needs more driving pressure to keep rejection performance at the same level, so a reading that climbs whenever household pressure dips, then settles back once pressure recovers, is just reflecting that relationship rather than signaling a fault (source: NU Aqua Troubleshooting Guide). A number that keeps creeping upward week after week, independent of pressure, is the more telling pattern and the usual sign of a membrane reaching the end of its working life. This article treats a rising number only as a symptom; for normal ranges and how to read your own TDS day to day, our guide to what TDS should read in RO water covers that in more depth.

Leaks, Drips and Loose Fittings

Most housing and fitting leaks come down to the same three causes: a worn or misseated O-ring, tubing that wasn't cut square or pushed fully into its fitting, or a housing cap that has worked loose over time and let the O-ring shift out of its seal (source: NU Aqua Troubleshooting Guide). That last cause is a reminder to recheck the cap periodically rather than treat the initial tightening at installation as the only time it needs attention; as a general caution, forcing a plastic housing cap past snug can also stress the seal, so the goal is a secure fit, not maximum force. Before assuming a part is cracked, isolate which section the leak actually comes from: the feed side, the filtered side, or the drain line, drying each in turn and running the system briefly to see where moisture reappears first, since a leak that looks like it's coming from a housing can trace back to a drain-line fitting a few inches away. A unit with built-in leak detection, such as the RO600, adds a layer here by flagging a leak before it's visible, which matters most for a drip that starts small inside a cabinet.

When It's a Cartridge Swap and When to Contact Support

Most of what's covered above resolves with a cartridge replacement once you've matched the symptom to the likely stage: a clogged prefilter for slow flow on both sides, a spent carbon stage for taste and odor, or a membrane nearing the end of its life for a persistent flow or TDS problem. On the RO600, the per-cartridge light flashing red at under 5% of its rated life is a direct cue to replace that specific stage rather than guess which of the three it might be, whether that turns out to be the PPC sediment and carbon cartridge for the prefilter side of things or the TC post filter when taste points to the carbon stage rather than the membrane. If you'd rather follow the physical steps for actually swapping a cartridge or the membrane, our step-by-step guide to changing RO filters and the membrane covers that part in full, and a regular preventive schedule rather than reacting to symptoms as they appear is the subject of our RO maintenance schedule.

There's a clear line, though, where it stops being a cartridge-level job. If a symptom persists after you've replaced the part the display or the checks above pointed to, that's a sign something else is going on, such as a valve or pump fault rather than a worn consumable. The same goes for any leak at a permanent plumbing connection, as opposed to the system's own fittings, since that's a plumbing job rather than a filter-change job. In either case, contacting support or a plumber is the sensible next step rather than continuing to open the unit on a guess. If you're still deciding whether the membrane itself needs cleaning or outright replacement once you've narrowed the cause that far, our guide on cleaning versus replacing an RO membrane walks through that decision, and if you want the fuller picture of how reverse osmosis and the RO600 work before troubleshooting one, our complete guide to reverse osmosis is the place to start.