Direct answer: Maintain a reverse osmosis system on the exact manufacturer’s schedule for its prefilters, postfilter, membrane, storage tank, and sanitation procedure. Replace a component sooner when the manual’s capacity, flow, pressure, water-quality, or diagnostic trigger is reached. There is no universal RO filter-change interval, and a TDS reading alone cannot prove that the water is safe.
An under-sink RO unit is a group of components, not one filter. It may include prefilters, a membrane, tank, postfilter, pump, remineralization stage, leak shutoff, or monitor. Each has its own service requirements. Start with the complete model number and current manual.
Make one model-specific service card
Keep this information near the unit or in a household maintenance file:
- manufacturer, exact system model, and serial number;
- stage order and the part number for each replacement element;
- certified listing and named reduction claims, if applicable;
- required calendar or treated-volume limits for each stage;
- membrane diagnostic method and threshold stated in the manual;
- sanitizing method, approved chemical, and required flushing sequence;
- baseline fill time, faucet flow, feed-water reading, and product-water reading taken under the manual’s test conditions;
- last service date, parts used, and next required trigger.
Do not assume cartridges are interchangeable because they fit. A substitute can change flow, sealing, pretreatment, or the evidence behind a certified claim. The cost of correct consumables and service is part of the reverse osmosis system cost over its useful life.
A practical RO maintenance schedule
The manufacturer supplies the interval; the owner tracks events around it.
| Trigger or observation | Check | Appropriate next step |
|---|---|---|
| A manual-defined date or gallon limit is reached | Correct stage and replacement part | Follow the model’s change and flush procedure |
| Product-water flow slows | Prefilters, feed valve, pressure, tank, membrane, faucet, and tubing | Diagnose in the order given by the manual rather than replacing parts at random |
| Taste or odor returns | Postfilter due status, sanitation record, stagnation, and source-water change | Service the specified component; use testing for unresolved safety concerns |
| Tank produces little usable water | Feed pressure, tank condition or precharge, shutoff valve, and membrane production | Follow the model’s diagnostic steps or request service |
| Drain flow is continuous or abnormal | Shutoff valve, flow restrictor, pressure, membrane, and tubing | Prevent water waste and diagnose promptly |
| Housing, fitting, or tubing leaks | Seating, O-rings, tubing cuts, pressure, and damaged components | Shut off the feed and repair before reuse |
| Product-water diagnostic no longer meets the manual’s criterion | Prefilters, operating conditions, membrane, and instrument method | Confirm test conditions, then service as directed |
After any service, record the parts, lot or model numbers, observations, and readings. A reliable history is more useful than trying to remember when the faucet “started feeling slower.”
Prefilters and postfilters
A sediment prefilter can protect downstream components from particles. A carbon prefilter may protect the membrane from substances it is not designed to tolerate. A postfilter usually treats water after storage. Exact functions depend on the system.
Do not stretch prefilter life because the membrane appears to be working. A neglected upstream cartridge can restrict flow or expose the membrane to conditions outside its design. Conversely, replacing every stage whenever one cartridge is due can waste usable components unless the manual specifies a bundled change.
During service, use clean handling practices, shut off and depressurize the unit as instructed, confirm stage order, inspect approved seals, and flush each component for the required amount or sequence. Never use an unrelated brand’s procedure as a substitute.
Membrane condition and replacement
Membrane life depends on the membrane type, feed-water chemistry, pressure, temperature, pretreatment, recovery, use, and maintenance. Replace it at the manufacturer’s interval or when the prescribed test shows that it no longer meets the model’s performance criterion.
A membrane check may compare feed-water and product-water conductivity or total dissolved solids under stabilized conditions. The readings should be taken with a suitable, calibrated meter and according to the manufacturer’s procedure. Temperature, pressure, recent stagnation, incomplete flushing, and a depleted prefilter can distort interpretation.
TDS is a broad conductivity-based estimate of dissolved ions. It does not identify lead, PFAS, microorganisms, pesticides, or other individual substances, and a low reading is not a safety verdict. A health-based concern requires the appropriate report, analytical test, and exact model claim—not simply a countertop meter.
Storage tank, faucet, and sanitation
The tank can influence delivered volume even when the membrane is functioning. Diagnose low output by considering tank pressure or bladder condition, feed pressure, shutoff operation, membrane production, and faucet flow together. Check or adjust precharge only if the manual gives an owner procedure, including whether the tank must be empty and which gauge to use.
Sanitize the system at the events and with the method stated by the manufacturer. Manuals differ on whether filters or the membrane remain installed, which solution is allowed, where it is introduced, how long it contacts the system, and how many tanks must be flushed. Mixing chemicals or applying a generic recipe can damage components or leave an unsafe residue.
Pressure, production, and TDS troubleshooting
Use a consistent diagnostic sequence:
- Confirm the feed valve is fully open and the unit is not intentionally shut down.
- Check for kinked tubing, a full leak tray, closed tank valve, or obvious leak.
- Verify prefilters are within their specified limits.
- Measure pressure only at the location and operating state the manual defines.
- Allow the system to stabilize and flush before collecting diagnostic readings.
- Compare feed and product readings using the manufacturer’s formula and criterion.
- Check tank delivery and drain behavior separately from membrane quality.
- Escalate if the result is outside instructions or the unit cannot be safely isolated.
A Houston address should be tied to its exact utility or private well when source water changes. Review the current report for that system or obtain targeted water testing if the concern is property-specific. A report for the City of Houston system does not describe every utility, MUD, or well in the metro area.
Leak and drain checks
RO systems contain many small tubing connections. After service, restore feed pressure gradually, dry all fittings, and inspect with the tank filling, the faucet running, and the faucet closed. Recheck later because a slow leak may not appear immediately. Never ignore water near an outlet, pump, or control module.
Drain water is normal during production, but continuous or changed drain behavior can indicate a problem. Use the model’s expected operating description; do not pinch or plug the drain line to stop apparent waste. The flow restrictor and air-gap configuration are functional parts of the system.
When professional service makes sense
Request help for repeated leaks, damaged housings, unknown tubing changes, persistent drain flow, failed shutoff, suspected tank failure, pump or electrical faults, sanitation concerns, or readings that remain outside the manual’s criteria after routine checks. Provide the model, photos, service history, pressure information, and feed/product readings when you request service.
If the equipment is undocumented or replacements are unavailable, compare repair with properly selected reverse osmosis systems whose claims, consumables, and service procedures can be verified.
Installation company disclosure: Water Filtration Houston provides water-treatment installation through a licensed and insured installer. This guide does not replace a property review, fit-for-purpose testing when needed, exact manufacturer documentation, or a written installation proposal.
Frequently asked questions
How often should reverse osmosis filters be changed?
Use the exact system’s calendar, gallon, flow, or diagnostic limits. Prefilters, postfilters, and membranes may have different triggers. Do not apply one brand’s schedule to another.
Does a low TDS reading mean my RO water is safe?
No. TDS estimates overall dissolved ionic content; it does not identify each substance or microorganism. Use the correct laboratory method for a specific health concern and verify the exact model’s certified claim.
Why is my RO faucet running slowly?
Possible causes include loaded prefilters, low feed pressure, a tank issue, a restricted tube or faucet, membrane performance, temperature, or valve position. Follow the model’s diagnostic order instead of assuming the membrane has failed.
Should the tank be emptied during maintenance?
Only as the manual directs. Emptying may be required for filter changes, sanitation, tank-pressure checks, or diagnostic work, but the sequence varies by system.
Can I use any replacement cartridge that fits the housing?
No. Use the specified part or a replacement explicitly approved in the manufacturer’s documentation. Physical fit does not establish equivalent performance or preserve certification.