Signs Your RO Membrane May Be Failing: A Hyderabad Homeowner Guide
Rising output TDS, reduced production and a taste change can indicate membrane trouble, but pre-filters, pressure, settings and seals also require checks.
What the RO membrane actually does inside your purifier
The RO membrane is a thin-film composite sheet wound tightly inside a cylindrical housing. It has microscopic pores approximately 0.0001 microns in diameter — roughly 500 times smaller than a bacterium. Feed water is pushed through this membrane under pressure (typically generated by a booster pump). Pure water molecules pass through; dissolved salts, heavy metals, fluoride, nitrate, and most contaminants are rejected and flushed out as drain water.
The membrane depends entirely on two conditions being correct: adequate feed pressure (minimum 0.5 bar, typically boosted to 3–6 bar by the internal pump) and clean pre-filtration (the upstream sediment and carbon filters must be in good condition). Without these conditions, even a brand-new membrane will underperform or degrade prematurely. Understanding this makes it clear why most slow-flow or high-TDS problems are actually pre-filter or pressure problems, not membrane failure.
Sign 1: Output TDS rises significantly without change in source
The most reliable indicator of membrane decline is a steady upward drift in output TDS when your inlet water TDS has not changed. Measure both inlet and outlet TDS with a handheld meter and calculate the rejection ratio: (1 - output/inlet) × 100. A healthy membrane with a TDS controller should show 75–90% rejection. If rejection drops below 70% and you have confirmed the TDS controller is at minimum bypass, the membrane or its seals require inspection.
Before concluding it is membrane failure, rule out two common confounders: the TDS controller setting may have been accidentally adjusted during a recent service visit (a technician turning a dial can raise output TDS by 50–100 ppm), and the TDS meter itself may be reading incorrectly. Test with a second meter or a reference water sample if in doubt. In Hyderabad, the most common cause of post-service TDS rise is a readjusted TDS controller, not a damaged membrane.
Sign 2: Purified water production rate drops noticeably
When a membrane begins to foul or scale, the effective filtration area decreases and production drops — the tank takes longer to fill. In Hyderabad's high-TDS borewell zones, calcium and magnesium salts from the source water crystallise on the membrane surface over time, progressively blocking its pores. This scaling process accelerates when upstream carbon filters are overdue for replacement and allow chlorine to contact the membrane, causing oxidative degradation.
The critical diagnostic question is whether flow drop is sudden or gradual. A sudden drop after months of normal operation almost always indicates a clogged pre-filter, not a failed membrane. Gradual worsening over 6–12 months, accompanied by rising TDS, suggests membrane ageing. Always check and replace pre-filters before spending Rs 1,200–2,000 on a new membrane — if clogged pre-filters are the cause, a new membrane behind them will underperform just as quickly.
Sign 3: Persistent taste change with rising TDS
A marked taste change — salty, mineral-heavy, or simply different from what your household is accustomed to — combined with rising output TDS is a meaningful sign. This combination is more diagnostic than taste alone because many factors unrelated to the membrane affect water taste: an exhausted post-carbon polishing filter, bacterial biofilm in a long-uncleaned storage tank, or a change in the source water chemistry (common during seasonal transitions in Hyderabad).
If output TDS has not risen but taste has changed, the membrane is unlikely to be the problem. Investigate the post-carbon filter (replace it annually), sanitise the storage tank, and check whether the building switched water sources recently. Tank biofilm is a very common cause of taste change in Hyderabad during summer when tanker water brings higher microbial load into a tank that has not been cleaned in over a year.
Sign 4: Abnormally high reject water with very little pure output
A healthy RO system produces roughly 3–4 litres of reject water for every 1 litre of purified output, depending on the membrane GPD rating and feed conditions. If you notice continuous or heavy drain water flow while production is minimal, the ratio has gone wrong. This is often caused by a blocked or kinked flow restrictor on the drain line — the restrictor creates backpressure that pushes water through the membrane; if missing or bypassed, most water exits as waste without filtration.
A stuck-open solenoid valve or failed check valve can also cause continuous drain water even when the tank is full. These are plumbing and valve issues, not membrane problems. Confirm the distinction: if output TDS is still low (membrane is working) but reject water is excessive, the flow restrictor or valve is the issue.
How to extend membrane life in Hyderabad conditions
The single most impactful action is replacing the upstream sediment and activated carbon pre-filters on schedule. In Hyderabad borewell areas, this means every 4–6 months rather than annually. An intact, functional carbon filter ensures chlorine never reaches the polyamide membrane — chlorine oxidation is the primary cause of premature membrane failure in urban Indian households that receive chlorinated municipal water.
For very hard water zones (Kompally, Alwal, Nallagandla, Lingampally where TDS frequently exceeds 700 ppm), consider installing an external sediment pre-filter (a 20-inch big blue filter housing) before the main purifier. This extends RO system life significantly. Also, avoid running the purifier at very low inlet pressure — consistently running below the minimum pressure threshold wears the booster pump faster and reduces the effective pressure across the membrane, reducing both rejection and lifespan.
When the membrane actually needs replacement
Replace the membrane when rejection ratio consistently stays below 70% despite confirmed good pre-filter condition, correct pressure, and correct TDS controller setting; or when flow rate has declined to less than 50% of the original rated output after pre-filter replacement confirmed it is not the issue; or when the membrane is over 3 years old with hard borewell water (regardless of apparent performance, because aged membranes develop micro-tears that TDS meters may not catch).
After replacement, always ask the technician to flush the system for 20–30 minutes, verify no leaks under operating pressure, and measure both inlet and outlet TDS. The fresh membrane should achieve 85–95% rejection (accounting for TDS controller bypass). If post-replacement output TDS is still unexpectedly high, check for O-ring sealing issues, a misaligned membrane housing, or an incorrect membrane specification for your model.
Frequently Asked Questions
How long does an RO membrane last in Hyderabad?
On HMWSSB municipal water (150–300 ppm) with regular pre-filter changes: 2–3 years. On high-TDS borewell water above 600 ppm: typically 12–18 months. Pre-filter discipline is the biggest factor — clogged carbon filters that allow chlorine breakthrough destroy membranes regardless of water quality.
Does high borewell TDS automatically mean the membrane is damaged?
No. High inlet TDS describes the source water, not the membrane condition. A membrane can perform well against 800 ppm inlet water if pre-filters are maintained and pressure is adequate. Output TDS and rejection ratio — not inlet TDS — indicate membrane condition.
Can the membrane fail even if no filter alert has come on?
Yes. Most home RO purifiers track filter usage by time or volume, not actual membrane rejection performance. A membrane can degrade without triggering any alert. Regular TDS monitoring (monthly) is the only reliable way to catch this.
