When to Change Your Water Purifier Filter: The Complete Replacement Schedule

Why Filter Replacement Is the Most Important Maintenance Task

Your water purifier is only as good as its filters. A clogged sediment filter forces your pump to work harder, shortening its life. An exhausted carbon filter lets chlorine through to your RO membrane, degrading it permanently. An aged UV lamp continues to glow while its germicidal output has dropped too low to kill pathogens. Most households replace filters too late — some never replace them at all.

The Filter Stages in a Typical RO System

A standard 6–8 stage household RO purifier uses these stages in order:

• Stage 1 — Sediment filter (PP/Spun) — removes sand, rust, large particles
• Stage 2 — Pre-carbon filter (GAC or Carbon Block) — removes chlorine, colour, odour
• Stage 3 — RO membrane — removes TDS, heavy metals, dissolved salts
• Stage 4 — Post-carbon filter — polishes taste and odour after RO
• Stage 5 — UV lamp — kills bacteria and viruses in stored water
• Stage 6 — UF membrane (some models) — final barrier against bacteria
• Stage 7 — Mineraliser cartridge (some models) — re-adds essential minerals

Filter-by-Filter Replacement Schedule

Sediment Filter — Every 3–6 Months

Catches the heaviest particle load and clogs fastest. In areas with iron-rich or turbid water, 3 months is realistic. Signs it is due:

• Water flow from the purifier noticeably slows
• Filter housing becomes visibly discoloured when opened

Cost: ৳150–৳300. Replace yourself — it just unscrews.

Pre-Carbon Filter — Every 6 Months

Removes chlorine before it reaches and damages the RO membrane. This filter has no visible sign of exhaustion — it quietly stops working while looking fine.

Rule: If you can smell chlorine in your purified water, your carbon filter is already past due.

Cost: ৳300–৳700.

RO Membrane — Every 12–24 Months

Test by comparing source water TDS against purified water TDS. A healthy membrane achieves 90–95% rejection. If source water is 500 ppm and purified water reads above 80–100 ppm, your membrane is losing effectiveness.

Signs it needs replacement:

• Purified water TDS rising steadily over several weeks
• Purification speed slowing significantly
• Unusual taste returning to purified water

Cost: ৳2,000–৳5,000 depending on membrane type (75 GPD, 100 GPD) and brand.

Post-Carbon Filter — Every 12 Months

Final polishing stage that removes remaining taste and odour from stored tank water. Do not skip it — tank water can develop off-flavours if this filter is exhausted.

Cost: ৳200–৳500.

UV Lamp — Every 12 Months

UV lamps degrade gradually — they continue to glow even when germicidal output has dropped dangerously. The safe lamp life is approximately 9,000–10,000 hours (12–14 months of continuous use).

Critical point: You cannot tell by looking at a degraded UV lamp that it is failing. Replace on schedule, not on visible failure.

Cost: ৳500–৳1,500.

UF Membrane — Every 24–36 Months

The most durable component in the system. Backwashing can extend life significantly.

Cost: ৳800–৳2,000.

Mineraliser Cartridge — Every 12 Months

As it depletes, your water will taste progressively flatter.

Cost: ৳400–৳800.

Your Complete Annual Maintenance Calendar

How to Cut Your Annual Maintenance Cost

• Buy generic compatible filters — branded replacements often cost 3–5x more than compatible generics of equal quality
• DIY the easy swaps — sediment, post-carbon and pre-carbon filters are straightforward to replace yourself with basic tools
• Compare AMC prices — get quotes from the authorised service centre and at least two independent businesses before signing
• Keep a log — write the installation date on each filter with a permanent marker when you change it

Warning Signs Your Purifier Needs Attention Right Now

Do not wait for your scheduled service if you notice any of these:

• Purified water has an unusual taste or smell
• Water flow has slowed significantly
• Your TDS reading on purified water has increased over recent weeks
• The UV lamp indicator light is off or the unit is making unusual noises
• It has been more than 12 months since any filter was changed

Any of these signs means at minimum a sediment and carbon filter change is overdue. Test your TDS before and after replacement to confirm the system is back to full performance.