— reviewed against the regs as they stand.
Why your condition says 110, not 125
The Building Regulations’ default water limit for new dwellings is 125 litres per person per day, but councils in water-stressed areas — much of the south and east of England — can require the optional standard of 110 l/p/d through a planning condition. If your decision notice mentions water efficiency, regulation 36(2)(b), or “110 litres”, this is what it means. Building Control will then expect your water calculation to demonstrate 110, not 125.
It is worth being clear about the mechanism, because it catches people out: the tighter number arrives through planning, but it is discharged through Building Regulations. Nothing in Approved Document G changes automatically because of where you are building. The trigger is the condition on your permission, not your postcode — so read the decision notice rather than assuming.
If you’re building in London, your policy says 105
London Plan Policy SI 5 requires residential development to achieve mains water consumption of 105 litres or less per person per day, excluding an allowance of up to five litres for external water consumption.
That looks like a third standard. It isn’t. The Part G calculation adds a fixed 5 l/p/d of external use at the very end, after the normalisation factor. So:
- 105 l/p/d excluding external use (how London writes it), and
- 110 l/p/d including external use (how the Building Regulations optional standard writes it)
are the same target, measured the same way. Run your calculation against 110 in the normal way and a London scheme is satisfied. The only thing to watch is that your submission makes clear which convention the figure on the front page uses, because a “105” and a “110” sitting in the same planning file have caused more than one unnecessary round of correspondence.
The proposed national cut to 105 l/p/d currently under consideration by Defra is a different thing again — that one is 105 including external use, and it isn’t in force. See Part G is heading for 105 litres for where that stands.
Is 110 hard to hit?
Harder than 125 — the 15-litre haircut removes most of the slack — but very achievable with deliberate fitting choices rather than exotic kit.
Start from the ordinary specification that lands at 123.9 l/p/d: a 6/4 dual-flush WC, 6 l/min basin taps, a 180 litre bath with a 10 l/min shower, an 8 l/min kitchen tap and unspecified white goods. You need about 14 litres. Here is one route:
- Shower 10 → 8 l/min — saves 7.95 l/p/d. The single biggest lever in the calculation.
- WC 6/4 → 4.5/3 — saves 4.69 l/p/d. Most of it comes from the part flush, which the methodology weights twice as heavily as the full flush.
- Basin taps 6 → 5 l/min — saves 1.44 l/p/d.
That is about 14 l/p/d of savings. Run properly through the methodology the dwelling lands at 109.9 l/p/d — a pass at 110, from three unremarkable specification decisions and no change to the layout.
Other things that help, roughly in order of value:
- Specify the white goods. Left blank, the calculation charges defaults of 8.17 l/kg and 1.25 l/place setting. Real appliances usually beat both — worth around 5 l/p/d where they’re genuinely part of the handover.
- Aerated basin taps at 4 l/min rather than 5, if the pressure suits.
- A standard-size bath rather than a statement tub — though with a shower present this is worth only about 1 l/p/d per 10 litres of capacity, so it’s a smaller lever than people assume.
- Don’t fit a waste disposal unit. It’s a flat 2.80 l/p/d penalty with nothing to offset it.
Where a client insists on the big shower or the big bath, the offsets have to come from everywhere else — or from rainwater or greywater harvesting, which the methodology credits and which sometimes turns an impossible spec into a pass. Both are capped at the demand they can actually displace, and the same WC demand can’t be claimed twice across two systems.
Check before you order sanitaryware
The expensive mistake is buying fittings first and calculating second. Run your intended spec through our free WaterMonkey calculator — set the target to 110, watch the live PASS/FAIL, and adjust before anything’s ordered. There’s a 110 l/p/d version of the calculator already set to the tighter target, and fitting-by-fitting explainers for showers, WCs and taps if you want to understand a line before you change it.
The Building Control-ready report is £25 +VAT when you need it. Tricky condition wording or a marginal spec? Send it to us and we’ll sort it.
Common questions
Why does my planning condition say 110 litres?
Because the council has applied the optional technical standard for water efficiency, which is available to local planning authorities in areas of water stress. It is imposed through a Local Plan policy or a condition on your decision notice, and once imposed your Building Regulations water calculation has to demonstrate 110 l/p/d rather than the 125 l/p/d baseline.
London says 105 litres — is that a different standard?
No, it is the same requirement expressed differently. London Plan Policy SI 5 requires mains water consumption of 105 litres or less per person per day excluding an allowance of up to five litres for external water use. The Part G calculation adds a fixed 5 l/p/d of external use at the end, so 105 excluding external and 110 including external are the same target. Run the calculation against 110 and you have satisfied both.
How much harder is 110 than 125?
Meaningfully harder, because an ordinary specification only passes 125 by about a litre. You need roughly 14 l/p/d of savings, which is achievable with deliberate but unexotic choices — an 8 l/min shower instead of 10, a 4.5/3 dual-flush WC instead of 6/4, and 5 l/min basin taps will do it between them.
Does the condition apply to the whole site?
Read the wording. Most conditions apply to all dwellings in the permission, but some are limited to a phase or to particular plots. Where several house types are being built you need the calculation to demonstrate the required target for each type.
Could the optional standard get tighter?
It is proposed. Defra has consulted on cutting the optional standard from 110 to 100 l/p/d alongside a cut in the baseline from 125 to 105. Nothing has changed yet — the government response is still awaited — but the August 2026 NPPF kept local water standards alive and left room for something stricter than 110 in areas of serious water stress.