When to change each part of your RO — and why the order matters.

The schedule

The intervals are the rated life of the LUXGEN cartridges. Your water moves them, and the symptoms column overrides the calendar every time.

Why the order matters

The three filters are a chain. Water hits sediment first, carbon second, the membrane last. Each stage exists to protect the one after it.

The sediment cartridge catches sand, rust and silt. If it clogs, flow drops and pressure at the membrane falls. If it is torn or bypassed, that silt lands on the carbon block and blinds it.

The carbon cartridge removes chlorine, and that is not only about taste. A TFC membrane is a thin polyamide film, and chlorine attacks polyamide. A membrane fed chlorinated water through a spent carbon cartridge loses rejection permanently: output TDS climbs and never comes back. Municipal supply is chlorinated by design, so that is exactly where the carbon stage earns its keep.

So the economics run backwards from what you would expect. The cheapest part protects the dearest. Skip the ₹190 sediment cartridge and the ₹220 carbon cartridge for a year to save money, and you buy a ₹650 to ₹900 membrane a year early. That is the whole argument of this page.

How to tell without guessing

Keep a TDS meter. On the day a new membrane goes in, run the purifier for an hour, then read the output. Write it down with the date, next to the feed reading. Read the output again once a month. When it has roughly doubled from the day-one figure — 30 to 60, or 60 to 120 — the membrane is done, even if the flow still seems fine. If your purifier has an adjustable TDS controller, leave it at the same setting for every reading, or the numbers mean nothing.

Sediment: look at it. A wound PP cartridge starts white. Brown across most of its length is overdue. A brown ring in the bowl says the same.

Carbon: smell the output. A chlorine smell in purified water means the carbon is exhausted. Do not wait for the calendar.

Pump: listen. A healthy pump is a steady hum. A rising whine, a rattle, or the pump running while the tank does not fill means the pump. It does not wear on a calendar, so replace it when it fails: LUX-PUMP-100, 24 V DC, 140 PSI, 1.5 LPM, ₹1,299. If a pump fails while the membrane is fresh, also check for a blocked sediment stage, which makes the pump work harder than it should.

Borewell versus municipal supply

Municipal. The water arrives filtered and chlorinated with little silt. The sediment cartridge lasts towards 12 months. The carbon stage is the busy one, because it is stripping chlorine every day. The membrane sees moderate TDS and should reach the 24-month end of its range.

Borewell. Unchlorinated, often silty, sometimes rusty, and the TDS climbs every summer as the water table drops. Sediment goes at 6 to 8 months. The carbon stage has less to do, but leave it in place: it still removes odour and organics, and borewells are sometimes shock-chlorinated. High TDS shortens membrane life towards the 18-month end. Above 2000 ppm, use the molded LUX-RO-100M and read the TDS chart on pre-softening.

Mixed supply — tanker plus bore, or municipal topped up from a bore in summer — gets borewell intervals. Plan for the worse water, not the better one.

A simple routine

1. Whenever you change anything, write feed and output TDS and the date on the housing with a marker.
2. Once a month: read the output TDS, smell it, glance at the sediment bowl.
3. Change sediment at 6 to 8 months on borewell or 12 on municipal, and carbon at 12. Do both at once if that is easier to remember.
4. Change the membrane when the output has doubled, or at 24 months, whichever comes first. The 80 vs 100 GPD guide covers which one.
5. Replace the pump when it fails.

Every part above is listed with its specification in the full range. If the cartridge you ordered last time did not fit, the Branded-Fit vs Universal-Fit guide explains why. If you are still choosing the purifier, start with the comparison.