Guide
Replacing water filter cartridges: when, how often and what it costs
Cartridges are the running cost of a water filter. Knowing how change dates are set, how to find the right cartridge and what to check about price and availability turns a vague worry into a figure you can plan around.
How long do water filter cartridges last, and how often should you replace them?
The manual for your exact model sets the schedule. Where it gives both a time limit (a number of months) and a volume limit (a number of litres), the cartridge is due for replacement at whichever arrives first.
Which one you reach depends on how much water goes through it. A household that uses little may hit the time limit long before the litres run out; a busy household may use up the rated litres well inside the time limit. To find out which applies to you, divide the rated litres by the litres you use in a day. Here is how that works for one hypothetical cartridge, rated at 1,500 litres or 6 months:
| Rated litres | Litres used a day | Months to use the rating | Which limit arrives first |
|---|---|---|---|
| 1,500 | 5 | 9.9 | time, after 6 months |
| 1,500 | 10 | 4.9 | volume, after about 4.9 months |
| 1,500 | 15 | 3.3 | volume, after about 3.3 months |
A system with several cartridges has several schedules, and they usually differ. Count each separately, as the running-cost calculator does.
Find the exact cartridge code
Look for the replacement code the manufacturer lists for your exact model and variant. It is usually in the manual or on the maker’s website, and often printed on the cartridge or housing. Places to check, in order:
- The manual or quick-start card, usually near the maintenance section.
- The label on the old cartridge or on the housing.
- The product page for your model on the maker’s own site.
- The maker’s support team, if the above disagree.
A cartridge that looks similar may not fit, and may not carry the same claims or ratings as the original, so match the code rather than the appearance.
Price, availability and assumptions
- Prices change. Look up the current price of the exact cartridge code when you compare, and note the date you looked.
- Check availability before you buy the system. A cheap filter is a poor deal if its cartridges are hard to get. Find the replacement in stock, and ask the maker how long they intend to keep supplying cartridges for the model.
- Sets, singles and bundles. Work out the cost of one complete change, including every cartridge the schedule calls for at that point.
- Write your assumptions down. The price, the interval and your daily use are what the total rests on. Change them in the calculator and see how much the answer moves.
Changing and cleaning
Steps differ from model to model, so follow the manual for each stage: turning off and releasing the supply where relevant, removing and refitting the cartridge, flushing a new one, and any cleaning or sanitising of housings, reservoirs or taps. If a step involves the plumbing and you aren’t sure of it, ask a qualified plumber. Note the date of each change and set a reminder for the next, which makes it easier to stay on schedule.
The Drinking Water Inspectorate’s guidance for England and Wales also stresses keeping up with replacement: domestic water filters and softeners. A cartridge past its rated life may not do what the maker says it does.
Counting replacements in the cost
To see what a filter really costs, add the replacements to the purchase price over the period you care about. After the set fitted at purchase, the number of paid changes depends on the interval:
| Change interval | By 1 year | By 3 years | By 5 years |
|---|---|---|---|
| Every 3 months | 3 | 11 | 19 |
| Every 6 months | 1 | 5 | 9 |
| Every 9 months | 1 | 3 | 6 |
| Every 12 months | 0 | 2 | 4 |
The calculator applies the same rules: sets included in the price are listed but not charged again, each cartridge follows its own schedule, a set due exactly at the end of a period belongs to the next period, and a missing input produces “incomplete” rather than £0.
Common questions
Can I use a cheaper compatible cartridge?
Third-party cartridges exist for some models. Whether one fits is one question; whether it carries the same claims or certificates as the maker’s own is another. Check that the listing names your exact model, compare any claims with the original’s, and read your warranty terms.
What if I miss a change date?
Change it as soon as you can and keep to the schedule from then on. The manual may say what to do after a long gap, such as extra flushing or cleaning, so check it.
Do I need to flush a new cartridge?
Many makers ask for it. The amount and method are model-specific, so follow the manual.
For fit and installation, see the under-sink guide and the countertop guide. To see how claims are labelled, read How we check.
Change intervals vary by model; the maker’s instructions for yours have the final say.