How often RO filters really need changing

Every purifier box prints a service interval. It is an average across the country, not a measurement of your water. Two homes in the same sector can be six months apart on a membrane, and the only way to know which one you are is to measure.

TDS is the number that matters

Total dissolved solids tells you how much mineral content the water carries. Anything between roughly 50 and 150 ppm at the tap is a comfortable range for taste and mineral content. A good technician measures it before and after servicing and shows you both readings — if nobody offers, ask.

A realistic schedule

• Sediment and carbon pre-filters: about every 6 months, sooner if your input water carries visible particles
• RO membrane: 12 to 18 months, driven by input TDS and how much water you actually run
• UV lamp, where fitted: about a year, because output drops long before the lamp stops glowing
• Tank sanitisation: at every service, not annually

Pre-filters are cheap and protect the membrane, which is not. Skipping pre-filter changes to save money reliably costs more, because the membrane takes the load instead.

Signs you are overdue

• Output has slowed noticeably — the tank takes much longer to fill
• Taste has changed, or the water has picked up a flat quality
• TDS at the outlet has climbed from where it used to sit
• The purifier runs far more often than it used to for the same consumption

On AMCs

An annual contract makes sense if it is specific about what is included. Ours covers four scheduled services with the standard filter set; the membrane and UV lamp are charged separately when they are actually due. Be wary of any contract that is vague about which parts are covered — that vagueness is usually where the cost lives.