125 litres per person per day, explained

Updated 21 August 2026 — reviewed against the regs as they stand.

Where the number comes from

Part G of the Building Regulations caps a new dwelling’s calculated water use at 125 litres per person per day. Nobody meters your actual usage — the figure comes from the official methodology, which multiplies each fitting’s consumption by a standardised “use factor” (how often a typical person uses it daily) and adds a fixed 5 litres for outdoor use.

So a 9 litres/minute shower, a 180-litre bath, a 4/2.6-litre dual-flush WC and so on each contribute their share, and the shares must total ≤125. (Some areas use the tighter optional 110 l/p/d standard — check your planning conditions.)

Which standard applies to you

There are three numbers in circulation and only one of them applies to your project today.

• 125 l/p/d — the Building Regulations baseline for every new dwelling in England and Wales. This is your target unless something says otherwise.
• 110 l/p/d — the optional technical standard. It only applies where a Local Plan policy or planning condition imposes it, which is common across much of the south and east of England and standard practice in London. It is a planning route into a Building Regulations requirement, so the trigger is your decision notice, not your postcode.
• 105 l/p/d — proposed, not in force. Defra has consulted on cutting the baseline from 125 to 105 and the optional standard from 110 to 100. The consultation closed in December 2025 and the government response is still awaited; implementation is intended during 2026 with a six-month transitional period. We’re tracking it in Part G is heading for 105 litres.

One thing not to assume: that a single national number is coming. The August 2026 NPPF kept local water efficiency standards on the table, including the possibility of something stricter than 110 in areas of serious water stress. For now, read the decision notice.

Where the litres actually go

The big three are showers, WCs and baths — together usually about two-thirds of the total. Taps and white goods matter less than people expect.

Here is what an entirely ordinary specification looks like: a 6/4 dual-flush WC, 6 l/min basin taps, a 180 litre bath with a 10 l/min shower over it, an 8 l/min kitchen tap, and unspecified white goods.

• Shower — 43.70 l/p/d before the final adjustments
• WC, full and part flush together — 20.60
• Bath — 19.80
• Washing machine (default figure) — 17.16
• Kitchen taps — 13.88
• Basin taps — 11.06
• Dishwasher (default figure) — 4.50

That totals 130.70. Multiply by the 0.91 normalisation factor and add the fixed 5 litres of external use, and the answer is 123.9 l/p/d — a pass, with 1.1 litres to spare.

That margin is the point of this page. A normal specification passes by about a litre. Which is why a late change to the sanitaryware can turn a compliant scheme into a non-compliant one, and why running the numbers before the bathroom order goes in is worth ten minutes of anybody’s time.

Practical rules of thumb

• The shower is the lever. Every litre per minute is worth roughly 4 l/p/d on the final figure. Dropping from 12 to 9 l/min usually fixes a fail on its own. See shower flow rate.
• The part flush is worth twice the full flush. The methodology assumes two part flushes for every full one, so a litre off the part flush is worth 2.69 l/p/d against 1.33 for the full. And a dual-flush WC beats a 6 litre single flush by about 5.4 l/p/d for no design compromise at all — see WC flush volume.
• Basin taps repay more than kitchen taps. A litre per minute off the basins is worth 1.44 l/p/d; the same litre at the kitchen sink is worth 0.40, because most of the kitchen line is a fixed allowance you can’t design out. See tap flow rates.
• A big bath is rarely fatal — unless there’s no shower. With a shower present the bath factor is only 0.11, so 10 litres of capacity is worth 1 l/p/d. Take the shower away and the factor jumps to 0.50, and the bath alone can eat two thirds of the allowance. See bath capacity.
• Unspecified white goods cost you. Leave them out and the methodology charges defaults of 8.17 l/kg and 1.25 l/place setting — about 19.7 l/p/d between them. Real specified appliances usually beat that. See washing machines and dishwashers.
• A waste disposal unit is a flat 2.80 l/p/d penalty with nothing to offset it. Worth knowing before one appears late in the kitchen design.
• Offsetting is allowed. Splash out on the shower and claw it back on WCs and taps. Rainwater or greywater systems are credited too, though they’re rarely needed just to hit 125.

See your own numbers

The fastest way to understand it is to try it: our free WaterMonkey calculator shows a live breakdown of where your litres go and a PASS/FAIL that updates as you change fittings. Experiment freely; the Building Control-ready report is £25 +VAT when you’re done. Or we’ll do it for you.