Replacement cartridges

Water filter cartridges: which one fits, and what they cost

Find the replacement for the under-sink filter you already own, or check what its cartridge costs before you buy the system. We cover the under-sink, countertop and gravity systems on this site. For each we list the cartridge to order, what it fits and doesn’t fit, the price we recorded and how often the maker says to change it. We don’t sell anything: the buttons go to the makers’ own pages.

Tap Sorted cartridge page · Updated

An open under-sink cupboard showing the waste trap and pipework, with a tape measure on the floor and no filter fitted

Affiliate disclosure. We may earn a commission if you buy through a link marked Affiliate link. This does not change the price you pay. Only the Doulton and Water-to-Go buttons on this page are affiliate links; every other link goes straight to the maker.

Choosing the right cartridge

Cartridges are not interchangeable by size or appearance. What matters is your housing model and the exact cartridge code the maker lists for it, so a “universal” cartridge that only matches the length is a risk. Work through these four steps:

  1. 1. Find your housing modelOn the housing, the manual or your order.
  2. 2. Check the cartridge codeUse the code the maker lists for that exact model and variant.
  3. 3. Choose the cartridgeMatch it to the code, then compare the price and change interval below.
  4. 4. Follow the flush instructionsFlushing is model-specific, so use your manual.

Which cartridge fits which system

Fit is set by the maker for each system, not by size. This table shows the exact models we have checked, with what each takes and what it does not take. Where we have not checked, it says so.

Which cartridge fits which system, prices read 16 October 2026
SystemTakesDoes not takeCost and change
Doulton KingfisherBiotect Ultra 2501 and Ultra SI 2505Ultracarb 9501, 9505 or M15; gravity UltraSterasyl 86742501: £29.45, every 6 months, 2,300 litres
Doulton HIP DUO2501 and 2505 SI, plus one DUO or TRIO pre-filter: 9A04, 9H04, 9F04, 9E04 or 9B04Ultracarb 9501, 9505 or 5594; gravity 8674 or 8B762501 as above; 9A04: £36.45, about every 3 months
Doulton countertop system2501 and 2505 SI onlyDUO pre-filters, gravity elements and Ultracarb2501: £29.45, every 6 months, 2,300 litres
British Berkefeld gravity systemsUltraSterasyl 8674 or UltraFluoride 8B76; never mix the twoBiotect Ultra and Ultracarb8674: from £23.95, rated 1,500 litres per element; replace every six months
Aquaphor Crystal SoloK2Not checkedK2: £22.99, nine months, 4,000 litres
Aquaphor Crystal three-stageThe K3, K2 and K7 setNot checkedSet: £57.99, nine months (sources conflict), 8,000 litres
Waterdrop WD-10UAWD-RF10The RF10-UF is a different cartridge, not interchangeableWD-RF10: £32.99, every 12 months
UK Water Filters anti-scale kitASC2000Not checked£29.97 on sale (usual £39.97), up to 6 months, or 3 if scale performance falls
Waterdrop C1SL countertop reverse osmosisC1RFG, not the C1RFC1RFC1RFG: £69.00, maker says 12 months or 1,100 US gallons; shown as sold out
Phoenix gravity filterSmartCarbon filtersNot checkedMaker says change every 12 months

Cartridges for the systems we cover

Prices are the sellers’ displayed prices on 16 October 2026 and change. The cards show the replacement cartridges themselves; check the model code against your housing before ordering. How we got these figures is in the under-sink comparison.

Doulton: which elements fit the Kingfisher

Doulton lists the Biotect Ultra 2501 and the Ultra SI 2505 as compatible with the Kingfisher, and not its Ultracarb 9501 and 9505, M15 or gravity Ultra Sterasyl 8674 elements. We give no performance claim for the SI 2505; see Doulton’s own description. The Kingfisher takes a cold line only. Doulton strongly recommends a matched tap, separate or three-way, and notes a maximum filter flow of 1.9 litres a minute, so an existing tap is not a universal fit; see fitting without drilling.

Common questions about water filter cartridges

Are water filter cartridges universal?

No. Matching length or thread is not enough: the housing model and the maker’s cartridge code decide what fits. A cartridge sold as “compatible” may fit physically and still lack the claims or certificates of the original, so check the listing names your exact housing.

Are water filter cartridges interchangeable?

Only when compatibility with the exact housing is confirmed. Some standard formats are shared, but matching a size alone does not establish compatibility or equivalent performance. Waterdrop’s WD-RF10 is not interchangeable with its RF10-UF, and Doulton’s Kingfisher takes only the Biotect Ultra 2501 and Ultra SI 2505.

Can you clean a water filter cartridge?

Only if the maker says so for that exact cartridge. A sealed cartridge cannot be restored by washing, and cleaning a cleanable ceramic element does not reset its life. The replacement and care guide has the full decision flow.

How long do water filter cartridges last?

Each maker sets a time limit, a volume limit, or both, and the earlier one applies. The card for each cartridge above shows the limits we recorded; how the earlier limit decides explains the rest.

Before you order

Before you fit a replacement

Follow the flushing and handling instructions for your exact cartridge. Cleaning a ceramic surface does not renew the carbon inside or reset a change date. Read the cleaning and replacement guide before opening the housing.

Filters for Water-to-Go bottles

This is a different product from the under-sink cartridges above. Water-to-Go filters fit its bottles, and each is rated for up to 200 litres; the maker’s pages are not consistent about time, as the Water-to-Go bottles guide explains. The twin pack is shown below.

Twin pack of two Water-to-Go replacement filters

Photo: Water-to-Go

Shop Water-to-Go replacement filters Affiliate link

Next steps

Sources

Read on 16 October 2026 from the makers’ own pages. How we check.