RO Filter & Membrane Replacement
A reverse osmosis system is a relay team: sediment and carbon stages protect the membrane, the membrane does the real separation, and a polishing stage finishes the taste. Each runs on its own clock. When owners learn the schedule, the system delivers lab-grade water for years; when they don't, the expensive membrane quietly pays for the neglected cheap stages.
Signs You Need This Service
An RO system due for service:
- The trickle at the RO faucet. Slow fill is the classic sign: spent pre-filters, a fading membrane or a tired tank bladder, in roughly that order of likelihood.
- Taste drifting back. Chlorine notes or flatness returning means the carbon stages are past their useful life, and the membrane behind them is now unprotected.
- TDS creeping toward tap levels. The measurable truth: product-water TDS climbing toward the feed number is the membrane reporting its own decline.
- The system running more, delivering less. Longer refill cycles and more reject water for the same glass: hydraulic signs the stages are loading up.
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This page covers keeping an installed system honest: which stages change when, what a TDS meter actually tells you, and the service that restores pressure and taste. Leaks and pressure faults belong to the RO repair page; choosing or installing a system is the RO hub's territory.
Common Causes
What actually wears the stages:
- Pre-filters die protecting the membrane. Sediment and carbon stages are sacrificial by design: they load with debris and chlorine so the membrane never sees either. Their death on schedule is success, not failure.
- Chlorine is the membrane's poison. Thin-film membranes tolerate almost no free chlorine; a spent carbon stage upstream shortens the membrane's life silently. That is the maintenance chain's whole logic.
- Hardness scales the membrane. In hard feed water, minerals concentrate at the membrane surface. Systems on hard supplies retire membranes faster, or earn a softener upstream.
- Storage-tank bladders age. The pressurized tank loses charge or its bladder stiffens, mimicking filter problems. It is the component owners forget the system has.
How a Plumber Diagnoses the Problem
What replacement service includes:
- Stages swapped by role. Sediment and carbon pre-filters on their schedule, the polishing post-carbon likewise, the membrane only on evidence. Sanitary handling, new O-rings seated, housings torqued by hand and not beyond.
- The TDS verdict. Feed and product water measured before and after: the rejection percentage names the membrane's condition in one number, replacing guesswork and calendar superstition.
- Sanitize and re-pressurize. The full loop is sanitized at membrane changes, the storage tank's air charge checked and set. Those are the two steps that separate service from cartridge-swapping.
- Leak-check under working pressure. Every opened housing and fitting watched through a full pressurize-and-fill cycle before the visit closes. The RO repair page exists for leaks; the service visit refuses to create them.
Frequently Asked Questions
How often do RO filters really need changing?
Pre-filters (sediment and carbon) on a regular schedule, commonly every six to twelve months depending on feed water and usage; the post-carbon polisher around annually; the membrane on evidence rather than calendar, typically every few years. The schedule protects the membrane, which is the one genuinely costly stage.
How do I know when the membrane itself is done?
Measure, don't guess: a TDS meter reading of product versus feed water gives a rejection percentage. A healthy membrane rejects the strong majority of dissolved solids; when product TDS climbs toward feed TDS despite fresh pre-filters, the membrane is finishing its service. That one measurement is the honest replacement trigger.
Why did my membrane fail early?
Almost always upstream neglect: a spent carbon stage let chlorine through, or hard feed water scaled the membrane surface. Membranes rarely die of their own age. They are killed by what the cheap stages stopped stopping. Keeping the pre-filter schedule is membrane insurance.
Can I change RO filters myself?
Cartridge swaps are owner-friendly on most systems: shut the feed, depressurize at the RO faucet, swap, hand-tighten. The steps owners skip (sanitizing at membrane changes, checking the tank's air charge, TDS verification) are what the service visit adds, and they are why professionally maintained systems taste right and run quiet.
Water flows slower even after new filters. Why?
Look past the cartridges: a storage tank with lost air charge or a stiff bladder fills and delivers poorly regardless of filter freshness, and a fading membrane throttles production. The tank's charge is checkable with a low-pressure gauge; the membrane answers to the TDS test. If both pass and flow still lags, the RO repair page takes over.
Service the System
List the system's stages if known, when anything was last changed, and your tap water's character.
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