Four under-sink systems, each picked for a different need: Aquaphor’s Crystal Solo for a budget kit with its own tap, Waterdrop’s WD-10UA if you’d rather use your existing tap, Doulton’s Kingfisher for an NSF listing that names the exact system, and an anti-scale kit from UK Water Filters if limescale is your reason. This is desk research, not hands-on testing: it rests on the sellers’ own pages, NSF’s registry and one credited US test of the Waterdrop.
Tap Sorted comparison · Updated
Prices checked
Picks by need
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NSF’s registry lists this Kingfisher with the Biotect Ultra cartridge, with reductions stated for chlorine taste and odour, particulates, cysts, lead and turbidity.
Drawback: The tap is extra, which makes it the dearest of the four at £299.90.
Subtotals at prices checked 16 October 2026: hardware plus replacement cartridges
System
1 year
3 years
5 years
Doulton Kingfisher with Biotect Ultra with tap
£329.35
£447.15
£564.95
Aquaphor Crystal Solo
£102.98
£148.96
£217.93
Waterdrop WD-10UA
£70.00
£135.98
£201.96
UK Water Filters Anti-Scale kit changed every 6 months
£126.97
£246.85
£366.73
UK Water Filters Anti-Scale kit changed every 3 months
£186.91
£426.67
£666.43
Each figure is a subtotal at the prices checked on 16 October 2026: hardware plus replacement cartridges. It leaves out fitting and any adaptors, the water itself, servicing and later price changes, so it isn’t the cost of a fitted system. The sums follow our running-cost calculator: the cartridge fitted at purchase is in the price, and each change counts when it falls due before the end of the period. 8 litres a day through the filtered tap is our assumption for drinking and cooking. It only matters where a maker gives a litre rating, and at this rate the Doulton and Aquaphor cartridges reach their time limits first. Over five years the cartridges alone cost £265.05 for the Doulton, £137.94 for the Aquaphor, £131.96 for the Waterdrop, £269.73 for the UK Water Filters (changed every 6 months), £569.43 for the UK Water Filters (changed every 3 months).
How they differ
The evidence gap matters more than the price gap
Only the Doulton has an exact-model independent entry that we have read: NSF’s listings name it and the reductions it covers. The other three rest on what their makers say, so treat their claims as unconfirmed rather than wrong.
NSF’s standards cover different things (42 covers aesthetic effects such as taste and odour, 53 covers listed health-related contaminants), and a listing applies only to the claims in it. Our certifications guide shows how to read one.
WRAS approval is a voluntary way for a maker to show that a fitting is of an appropriate quality under the water fittings regulations. It isn’t a mandatory approval and says nothing about how well a filter works. We didn’t check WRAS entries for these four. What matters in your home is that the installation meets the regulations that apply in your area; the under-sink guide covers who to ask.
Third-party testing is thinner still. We found one credible physical test of an exact model name, TechGearLab’s of a US Waterdrop WD-10UA, and it found no lead reduction. It was a US unit, so we treat it as a caution, not a UK result. For the other three we found no credible exact-model physical test in our searches so far.
Hardware is only like-for-like once the tap is counted
The Kingfisher is sold without a tap, so we added Doulton’s pillar tap (£44.95) to get £299.90. The Aquaphor and the UK Water Filters kit include theirs, and the Waterdrop uses the tap you already have. None of the totals include installation, which depends on your pipework and on whether you use a plumber.
If limescale is the reason
The Doulton listing doesn’t include hardness, and nothing we recorded for the Aquaphor or the Waterdrop is a hardness claim, so none of the three should be bought for scale. The UK Water Filters kit is the one aimed at it, but its own page says performance varies with your water. Our hard water guide explains what filters and softeners can and can’t do.
Dedicated tap (sold separately)Independently listedModel Kingfisher W9330300
A cartridge-and-installation-kit system that leaves the tap to you. Priced with Doulton’s pillar tap so it compares fairly with kits that include one.
Evidence basis. Manufacturer pages and instructions, plus NSF listings for the exact system. No third-party physical test found in our searches so far.
Clearest independent certification support. NSF’s registry lists this Kingfisher with the Biotect Ultra cartridge, with reductions stated for chlorine taste and odour, particulates, cysts, lead and turbidity. The cartridge instructions state capacity and flow, and the replacement cartridge is a plain £29.45 purchase.
Price
£299.90, made up of the Kingfisher system with cartridge and installation kit (£254.95[1]) and Doulton pillar tap (£44.95[2]), before fitting. Doulton’s terms of supply say prices include UK VAT where it applies. Regular prices, no subscription or discount. Seller: Doulton.[1][2][3]
Biotect Ultra 2501 cartridge, installation kit. No tap: a pillar tap is £44.95 extra.[1]
Replacement
Biotect Ultra 2501 (W9123050-01): £29.45 every 6 months, rated 2,300 litres. Doulton’s FAQ says to change it every six months. The instructions give 2,300 litres (600 US gallons) and 1.9 L/min.[4][5]
Check the current installation drawing and the clearance needed to remove the cartridge before you measure the cupboard. Doulton’s web page labels the dimensions inconsistently, so none is quoted here.[1]
NSF lists “Kingfisher + Biotect Ultra W9123050” (600 US gallons at 0.5 gpm). Standard 42: chlorine taste and odour; Class I particulate. Standard 53: cyst, lead, turbidity. Standard 372 relates to the lead content of the materials, not to lead removal. NSF names the Kingfisher with the Biotect Ultra W9123050 cartridge, which is the cartridge supplied with and replaced in this system.[13][14]
Pros
The only system here whose exact model appears in an independent registry.
The cartridge instructions give capacity and flow, and Doulton’s page gives a recommended pressure.
Replacement cartridges are a one-off £29.45 purchase with no subscription.
Cons
The highest hardware cost of the four, because the tap is extra.
The listed claims don’t include hardness, so it isn’t a limescale answer.
Think twice if you want one price that includes the tap, or mainly want to tackle limescale.
Not confirmed: Warranty and WRAS approval were not checked.
Budget kit with its own tap. £79.99 includes the tap and the first cartridge, with free delivery to the UK mainland. Its K2 replacement is £22.99, the lowest of the four, on a cautious nine-month cycle.
Price
£79.99. Aquaphor’s pages don’t say whether the price includes VAT, so this is the displayed UK price. Displayed price. Seller: Aquaphor.[6][7]
Delivery
Free delivery to the UK mainland; Highlands and Isle of Man may cost extra.[7]
In the box
tap, K2 cartridge. A drinking-water tap is included.[6]
Replacement
K2: £22.99 every 9 months, rated 4,000 litres. The product page gives 4,000 litres and a nine-month cycle. An older official manual says a year, so the shorter, current figure is used.[6][8]
Fit
Uses its own tap, so the sink or worktop needs a tap hole.[6]
Aquaphor’s pages give conflicting flow rates, so none is quoted.[6]
Lowest hardware price, no extra tap. £70.00 is the lowest price of the four, and it works through the tap you already have. It was in stock with free standard delivery to eligible UK addresses when checked (some postcodes, including BT, are excluded).
Price
£70.00. The page doesn’t state the tax position, so this is the displayed UK price. Standard price. A 15% checkout code lowers it to £59.49; this page uses £70.00. Seller: Waterdrop UK.[9]
Delivery
Free standard delivery to eligible UK addresses in 2 to 4 working days; the seller’s footer excludes some postcodes, including BT (Northern Ireland), so check yours.[9][15]
In the box
filter. No extra tap: it works through your existing tap.[9]
Replacement
WD-RF10: £32.99 every 12 months. The FAQ says 12 months. The page’s capacity figures disagree (8,000 US gallons in the FAQ, 11,000 on a banner, 30,000 litres on the variant label), so the 12-month figure is used and no capacity is claimed.[9][10]
Fit
Connects to the existing cold line and uses the existing tap.[9]
Pressure range in the FAQ: 10 to 125 psi (about 0.7 to 8.6 bar).[9]
Waterdrop’s NSF wording is the maker’s own. An attempt to look the model up in an independent registry didn’t return a result, so this is unconfirmed; it is not a finding that the model is uncertified.
Third-party test
A US-market review by TechGearLab (Austin Palmer and Lissette Velasquez, 15 July 2026) tested a WD-10UA (US unit). Over several metals test rounds it found no lead reduction and a modest improvement in chlorine taste. Installation needed the right adaptor, and it found no filter-change indicator. This was a US unit under the reviewer’s own conditions, so it doesn’t show how the UK model performs or what it is certified for: read it as a caution, not a UK performance figure. TechGearLab says it buys the products it tests and is funded by affiliate links.[16]
Pros
The lowest hardware price of the four.
No extra tap hole: it uses the tap you already have.
In stock with free standard delivery to eligible UK addresses when checked.
Cons
The product page’s capacity figures conflict.
Its NSF wording is the maker’s, with no independent registry entry confirmed.
Whether it suits your existing tap isn’t something we could check; confirm with Waterdrop.
The one third-party test we found, of a US unit, found no lead reduction; treat it as a caution rather than a UK figure.
Think twice if you need independently confirmed performance claims, or need a published, consistent capacity before you buy.
Not confirmed: Capacity, VAT basis, warranty and WRAS approval are not confirmed.
Worth a look if limescale is the reason. It is sold specifically for limescale, and the £97 kit includes the tap, housing, cartridge, tubing and connector, with delivery and VAT included. The page admits the cartridge may need changing at three months, and the costs below show both cases.
Price
£97.00. The page says VAT is included. October sale price; the page’s usual price is £137. Seller: UK Water Filters.[11]
Swan Classic tap, housing, ASC2000 cartridge, tubing, connector. A Swan Classic tap is included; an existing mixer tap is not compatible.[11]
Replacement
Anti-Scale cartridge (ASC2000): £29.97 every 6 months. Up to six months, but the page says scale performance can fall to three months depending on your water. Both are costed. October sale price; usual £39.97.[12]
Fit
Needs its own tap; an existing kitchen mixer tap is not compatible.[11]
The saddle connector is for copper pipe with about 5 cm (2 in) exposed; plastic pipe needs an adaptor or a plumber.[11]
Aimed at reducing limescale, with a stated cartridge life of up to six months.[11][12]
Independent listing
No exact certificate was confirmed, so the maker’s performance figures are not repeated here.
Pros
Tap, housing and the first cartridge are included, with delivery and VAT, at £97 on sale.
The only product here sold specifically for limescale.
The page is open about the cartridge possibly needing changing at three months.
Cons
Scale performance varies with your water, so the running cost is a range.
A separate tap is needed, and the connector suits copper pipe only unless you add an adaptor.
No independent certification confirmed, and the kit price is a sale price.
Think twice if you have plastic pipework and want to avoid a plumber, or expect whole-house softening or a cartridge guaranteed to last six months: this kit treats one tap’s water, and the page shows the cartridge may need changing sooner.
Not confirmed: Warranty is unclear (the page shows conflicting lengths) and WRAS approval was not checked.
Not included
BRITA mypure SLIM V-MF. BRITA’s page marks the system as discontinued, although refills are still sold, so we haven’t recommended it.[17]
How this was compared
Facts come from the sellers’ own pages, the cartridge instructions and NSF’s listings, all read on 16 October 2026 and cited beside each fact. Prices are the displayed UK price without coupons. “Maker’s claims” are what a manufacturer says; “independently listed” means a registry entry names the exact model and its claims. For fit and plumbing, read the under-sink guide; for how we label evidence, How we check.
