Two taps or one lever? The basin answers that before your budget does. A basin with two tap holes takes a pair of pillar taps or a two-hole mixer, and a basin with one hole takes a mono mixer. This guide settles basin mixer or pillar taps, with waste, pressure and the Water Regulations covered.
Quick answerChoose a mono mixer when the basin has one tap hole and you want a waste in the box. Choose pillar taps when the basin has two holes, or when hot and cold come from different sources, because the water only meets in the bowl. Check the hole count, the waste and the supply pressures before you order.
Pillar pair or mono mixer: what you are buying
Pillar taps are two separate taps, one hot and one cold, each fixed through its own hole. The water meets in the basin, not in the taps. A mono basin mixer is one body with one lever, and it blends the supplies inside before one stream leaves the spout.
Our basin taps range lists 59 products, including Ideal Standard, Grohe and Aqualisa taps. The Ideal Standard Calista range shows the split neatly. The Calista basin pillar taps (B1146AA) are a pair for two holes. The Calista single lever basin mixer (B1148AA) is one hole with a pop-up waste.
Basin mixer or pillar taps: the quick comparison
The table uses one range so the comparison is fair. Read the spec for your exact model, because hole count and waste change from product to product.
| Question | Pair of pillar taps | Mono basin mixer |
|---|---|---|
| Tap holes needed | Two | One |
| Where hot and cold meet | In the basin | Inside the tap body |
| Waste in the box | No, on the Calista pair (B1146AA) | Pop-up waste on the Calista mixer (B1148AA) |
| Flow regulator fitted | 4 l/min on the Calista pair | 5 l/min on the Calista mixer |
| Check valves | Not written for separate taps | Single check valves on the supplies |
| Listed price, 6 November 2026 | £86.39 for the pair | £101.33 with waste |
Check the basin first: holes, overflow and waste
Count the tap holes before you look at a single tap. The listing states what each tap needs: two for the Calista pillar pair, one for the Calista mixer and one for the Grohe Eurosmart 32467243L.
- Count the tap holes in the basin. Two holes means pillar taps or a two-hole mixer. One hole means a mono mixer.
- Look for an overflow slot at the back of the bowl. If there is one, you need a slotted waste.
- Check whether the tap includes a waste. The Calista pair and the Grohe Eurosmart 32467243L do not. The Calista mixer has a pop-up waste.
- Add the waste to the same order, so the first fix is not held up.
The basin wastes collection has 11 products, with slotted, clicker and pop-up types. The Ideal Standard traditional slotted basin waste (E6760AA) is £25.82 on 6 November 2026.
Trade tipA one-hole mixer on a two-hole basin leaves a spare hole to blank off. A pillar pair on a one-hole basin cannot fit at all.
Water Regulations: when a mixer needs check valves
The Water Supply (Water Fittings) Regulations 1999 cover England and Wales. Scotland and Northern Ireland have their own rules. Schedule 2 paragraph 15 requires backflow prevention, so water cannot flow back into the supply.
Water Regs UK says single check valves go on the pipework supplying a single-flow mixer tap. The reason is to stop cold pressurising the hot supply, and hot water reaching the cold mains, under fault conditions. It separates these taps from dual-flow taps, which keep separate water paths to the spout.
RuleMixer instructions also ask for hot and cold at reasonably balanced pressures from a common source. Where they are unbalanced, a check valve or equivalent goes on both inlets.
Unbalanced means a tank-fed cold tap with a mains-fed hot supply from a combi, or the reverse. A pair of pillar taps has two separate waterways, so the mixer requirement is not written for them.
Watch outThe Calista and Eurosmart listings do not say whether check valves are supplied. Check the instructions before you quote a job.
Pressure and flow: read the minimum, not the headline
Both styles suit low pressure, but the figures differ. The Calista pair has 4 l/min regulators and the Calista mixer has 5 l/min. Grohe lists the Eurosmart 32467243L, from the Grohe basin taps range, at a maximum 5 l/min at 3 bar and designed for low pressure systems.
Listed minimum pressures run from 0.1 bar to 0.5 bar across the Calista listings and guides, so use the maker's datasheet for your model. Our low pressure guide covers gravity-fed, combi and unvented systems. The Eurosmart also has an integrated temperature limiter and an adjustable flow limiter.
Worked example: a ten-room refit
Say you are replacing ten basins and the tap holes are still your choice. Compare the cost per room, using listed prices on 6 November 2026:
- Pillar pair: £86.39 for the Calista pair plus £25.82 for a slotted waste is £112.21 a room, or £1,122.10 for ten.
- Mono mixer: £101.33 for the Calista mixer with its pop-up waste is £1,013.30 for ten.
- Difference: £108.80 across the ten rooms, before fittings and valves.
The mixer is cheaper here because the waste is in the box. The pillar pair earns its place when hot comes from a combi and cold from a loft tank, because there is no mixing fitting to protect.
Where basin tap installs go wrong
- Wrong hole count. A pillar pair needs two holes. A mono mixer needs one.
- No waste ordered. The Calista pair and the Eurosmart come without one.
- Slotted or unslotted mismatch. A bowl with an overflow slot needs a slotted waste.
- Unbalanced supplies. A mixer on tank-fed cold and mains-fed hot needs check valves on both inlets.
- Pressure ignored. Compare the minimum pressure with the system before you order.
Buyer's checklist
- Count the tap holes and look for an overflow slot.
- Confirm whether the tap includes a waste, and which type the bowl needs.
- Check whether hot and cold come from the same source.
- Compare the listed minimum pressure with your system.
- Read the instructions for check valves before you quote.
Related reading
FAQs
A mono mixer uses one hole and takes less deck space, so it suits a narrow basin with a single tap hole. Pillar taps need two holes and room between them. The hole count in the basin spec decides the choice before style or price does.
The check valve requirement is written for single-flow mixer taps, where hot and cold meet inside the fitting. A pair of pillar taps keeps the water apart until the basin. Backflow prevention still applies, so follow the instructions supplied with your taps.
Often, but check first. A one-hole mixer leaves the second hole open, which needs a blanking cap, and the tap base must sit cleanly over the hole it uses. If the hole spacing is unusual, choose a two-hole mixer or pillar taps instead.
It depends on the model. The Ideal Standard Calista single lever mixer (B1148AA) includes a pop-up waste. The Calista pillar pair (B1146AA) and the Grohe Eurosmart 32467243L do not, so you need to add one. Each listing states whether a waste is included.
Minimum pressure depends on the model, and listings for the Calista taps range from 0.1 bar to 0.5 bar. Grohe says the Eurosmart 32467243L is designed for low pressure systems. Check the maker's datasheet against your system pressure, especially on gravity-fed hot water.
The Water Supply (Water Fittings) Regulations 1999 apply in England and Wales. Scotland has its own Water Byelaws, and Northern Ireland has separate regulations. Manufacturers print the mixer tap requirements in their instructions, so follow the sheet supplied with your tap wherever you work.
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