Troubleshooting the RO Triangle: Common Issues & FixesReverse osmosis (RO) systems rely on a set of interconnected parts that together determine performance, water quality, and efficiency. The term “RO Triangle” describes three core elements that must be balanced for the system to work well: membrane quality and condition, feed water characteristics and pressure, and pre/post-filtration & flow-control components. When any one corner of this triangle is off, the whole system’s performance degrades. This article explains common problems tied to each corner, how to diagnose them, and practical fixes — from fast user-level steps to service-level repairs.
What is the RO Triangle?
The RO Triangle is a helpful mental model: imagine each corner representing one crucial area.
- Membrane — the semi-permeable element that removes dissolved solids.
- Feed water (pressure & quality) — incoming water characteristics like TDS, hardness, chlorine, and pressure.
- Pre/post-filtration and flow control — sediment/carbon prefilters, check valves, flow restrictor, faucet, storage tank, and tubing.
All three interact: low pressure reduces membrane rejection; poor prefiltration shortens membrane life; a clogged flow restrictor or malfunctioning valve affects tank filling and flush cycles.
Signs of Trouble & How to Diagnose
1) Low production (slow flow)
Common symptoms: very slow faucet flow from RO, tank not filling, or long wait for water.
Likely causes:
- Low feed pressure.
- Clogged sediment or carbon prefilter.
- Fouled or aged RO membrane.
- Faulty or blocked flow restrictor.
- Partially closed shutoff or kinks in tubing.
Diagnosis checklist:
- Measure feed pressure (ideal 40–80 psi for typical household RO).
- Replace prefilters if >6–12 months since last change.
- Remove prefilters and observe if flow improves (short test).
- Check for kinks in tubing and ensure valves fully open.
- Inspect and, if possible, remove flow restrictor to verify it’s not clogged.
Fixes:
- Increase feed pressure with a booster pump if pressure is below recommended.
- Replace clogged prefilters or membrane (see TDS check below).
- Clear/replace flow restrictor.
- Ensure tubing runs and fittings are unobstructed.
2) High TDS (poor rejection)
Symptom: filtered water has unexpectedly high TDS or tastes salty.
Likely causes:
- Membrane failure, fouling, or end-of-life.
- High feed TDS beyond membrane’s effective range.
- Damaged O-rings or improper sealing allowing bypass.
- Incorrectly installed membrane or wrong membrane type (e.g., low-rejection model).
Diagnosis checklist:
- Measure feed TDS and product (permeate) TDS with a TDS meter. Percent rejection = (Feed TDS − Permeate TDS) / Feed TDS × 100.
- Compare measured rejection with membrane’s rated rejection (typically 90–99% for good RO membranes).
- Inspect membrane housing for leaks and proper seals.
- Confirm membrane model matches system specifications.
Fixes:
- Replace membrane if rejection is low and prefilters are clean.
- Ensure proper membrane seating and replace any worn O-rings.
- If feed TDS is extremely high (e.g., >1,000 ppm), consider a high-rejection membrane or pre-treatment (water softener, brackish-water RO, or specialized membranes).
- Clean membrane if fouling (scaling, organics) is reversible — follow manufacturer’s chemical cleaning procedure (acid for scaling, alkaline/oxidizer for organics) or hire a pro.
3) Constantly full/never full tank or continuous drain flow
Symptom: Tank never fills or system produces continuously (no shutoff).
Likely causes:
- Faulty automatic shutoff valve (ASO).
- Malfunctioning tank check valve or bladder tank failure.
- Worn or stuck float/valve in the faucet assembly.
- Flow restrictor missing or bypassed, preventing backpressure build-up to close ASO.
Diagnosis checklist:
- Observe if water is continually flowing to drain when faucet is closed.
- Check tank air pressure (empty tank, measure with tire gauge) — typical precharge ~5–7 psi when tank is empty.
- Inspect ASO and tubing between membrane and ASO for blockages.
- Remove flow restrictor (brief test) to see if behavior changes.
Fixes:
- Replace ASO valve if it doesn’t shut off when tank is full.
- Repair or replace tank bladder or tank if the precharge is incorrect or waterlogged. Set empty tank pressure to recommended value (usually ~5–7 psi).
- Reinstall/replace flow restrictor to restore proper backpressure.
- Replace faulty faucet valve components.
4) Leaks and dripping
Symptom: Visible leaking from fittings, housings, or faucet.
Likely causes:
- Loose fittings, cracked housings, or deteriorated O-rings.
- Improperly seated cartridges or membrane.
- Cracked tubing from stress or freezing.
Diagnosis checklist:
- Visually inspect housing, connectors, and tubing for wetness.
- Tighten quick-connect fittings firmly (push-to-seat then pull gently to confirm).
- Check O-rings in housings and the membrane cap for nicks or misplacement.
- Inspect for hairline cracks in housings.
Fixes:
- Replace damaged housings, O-rings, or tubing segments.
- Use plumber’s tape on threaded fittings where appropriate (but not on quick-connect fittings).
- If freeze damage is present, replace affected components and protect system from freezing.
5) Bad taste, odor, or chlorine breakthrough
Symptom: Off smell or taste in RO product despite membrane.
Likely causes:
- Saturated/expired carbon prefilter or postfilter (taste/odor filters).
- Chlorine bleach damage to membrane (if no catalytic carbon prefilter).
- Bacterial growth in tank or lines.
Diagnosis checklist:
- Note when prefilters were last replaced (carbon life often 6–12 months).
- Smell/taste test raw feed vs. product. If chlorine present in feed but also in product, pre-carbon failure likely.
- Inspect for slimy biofilm when changing filters.
Fixes:
- Replace carbon prefilters and postfilters. Use a catalytic carbon prefilter where chloramine/chlorine exist.
- Sanitize system and tank: follow manufacturer steps (bleach rinse at appropriate dilution, then flush thoroughly) or use recommended sanitizing agents. Replace tank if contaminated beyond cleaning.
- Ensure regular maintenance schedule to prevent bacterial buildup.
6) Noisy system or sputtering
Symptom: Gurgling, hammering, or irregular flow from faucet.
Likely causes:
- Air trapped in lines after filter change.
- Low tank precharge causing water-air oscillation.
- Cavitation in booster pump (if present) due to low inlet pressure.
Diagnosis checklist:
- After filter changes, open faucet to purge air thoroughly.
- Check tank pressure with tank emptied.
- Listen at pump inlet for cavitation; measure inlet pressure.
Fixes:
- Purge air by opening RO faucet until steady stream.
- Adjust tank precharge to recommended psi.
- Fit a larger inlet or remedy low-pressure causes for pump; ensure pump is properly sized and installed.
Maintenance Best Practices (prevent many issues)
- Replace sediment & carbon prefilters every 6–12 months; replace RO membrane every 2–5 years depending on feed water and usage.
- Keep an inline TDS meter and measure periodically. Record feed and product TDS to spot declining rejection early.
- Check tank precharge annually.
- Sanitize system and replace postfilters annually or when taste/odor returns.
- Use quality replacement parts (membrane rated for your feed, OEM housings and O-rings).
- If feed water contains high chlorine, chloramines, iron, or hardness, pre-treatment (softener, iron filter, catalytic carbon) will extend membrane life.
Quick troubleshooting flow (short checklist)
- Confirm faucets and valves are open, inspect tubing for kinks.
- Check feed water pressure; target 40–80 psi.
- Replace prefilters if overdue.
- Measure feed and RO TDS; calculate rejection.
- Check tank precharge and ASO operation.
- Replace membrane if rejection low after other fixes.
- Sanitize if taste/odor or suspected bacteria.
When to call a professional
- Chemical cleaning of membrane (requires proper acids/alkalines and handling).
- Complex feed-water pretreatment installation (softeners, iron filters, UV).
- Persistent leaks inside housings or cracked manifolds.
- Booster pump troubleshooting involving electrical components.
Troubleshooting the RO Triangle means checking membrane, feed, and flow-control components in concert rather than in isolation. Use routine maintenance, simple diagnostic checks (pressure, TDS, tank pressure), and targeted replacements to fix most common problems and keep your RO system producing clean, great-tasting water.
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