There is no universal “change every six months” rule
Service intervals depend on the product, feed water, cartridge capacity, household use, chlorine exposure, hardness, pressure and design. Treat the manufacturer's schedule as the baseline, then use permitted performance checks—such as rejection trend, flow and filter-life indicators—to spot abnormal behaviour.
What each service item is protecting
| Component | Job | What neglect can look like |
|---|---|---|
| Sediment prefilter | Protects downstream stages from particles | Pressure/flow loss, premature fouling |
| Carbon prefilter | Reduces chlorine/taste compounds; protects chlorine-sensitive membranes | Chlorine breakthrough, membrane damage risk |
| RO membrane | Main dissolved-solids separation | Higher permeate TDS, reduced rejection/production |
| Post-carbon | Taste polishing | Taste/odour changes |
| Remineralisation stage | Adds selected ions | Changed taste/mineral output |
| Tank/lines/dispenser | Stores and delivers finished water | Stale taste, hygiene risk if maintenance is poor |
Sanitising is not optional housekeeping
DWI technical guidance warns that inadequate cleaning of RO storage tanks and pipework can allow significant bacterial proliferation. Follow the exact sanitising procedure for your model: the correct chemical, concentration, contact time, flushing and cartridge handling matter. Do not improvise with household cleaners inside a drinking-water system.
After a holiday or long period of non-use
Standing water is different from a system in daily use. Follow the manufacturer's restart procedure. Some countertop manufacturers specify emptying, filter storage or rinse cycles after defined periods. If a cartridge has exceeded the maker's non-use limit, replace it rather than trying to “flush it back to life”.
Use TDS as a trend, not a verdict
Record feed and pre-remineralisation permeate TDS periodically if your system allows it. Calculate rejection with our TDS tool. A gradual change is more informative than comparing today's reading with somebody else's internet screenshot.
Slow flow: likely causes
Cold feed water naturally reduces membrane production. Low inlet pressure, clogged prefilters, a depleted/incorrectly pressurised tank, scaling/fouling or a restriction can also reduce output. Direct-flow and tank systems behave differently, so troubleshoot in the order specified by the maker.
Bad taste or smell
First establish whether the issue is present in the incoming cold tap. If it is new and strong, contact the water supplier. If it appears only after the RO system, stop treating the filter as automatically innocent: overdue cartridges, stale storage, new-filter flushing and sanitation all deserve attention.
Leaks
Shut off the water/electricity as appropriate and follow the product's emergency instructions. Push-fit tubing must be cut square and fully seated; O-rings need correct placement and condition. A slow leak inside a cupboard can cause far more damage than the cost of a professional installation.
Keep a service log
Record installation date, cartridge changes, sanitation, TDS/rejection, unusual symptoms and parts fitted. It turns maintenance from guesswork into evidence and makes warranty/support conversations much easier.
Sources and further reading
For factual claims that matter to health, regulation or product performance, we prefer primary and official sources. Useful references for this guide include:
- Drinking Water Inspectorate — Physical removal of contaminants
- Drinking Water Inspectorate — Domestic water filters and softeners
- NSF — NSF/ANSI 58 reverse osmosis systems
- Water Supply (Water Fittings) Regulations 1999 — legislation.gov.uk
Related guides
Last reviewed: 6 October 2026. This guide is written for a UK audience. Always follow current supplier, regulator, manufacturer and healthcare advice where it applies.