If you’ve done a Part G water calculation in the last decade, you know the number: 125 litres per person per day. It’s been the baseline since the standard came in, with an optional tighter standard of 110 l/p/d that councils can require through their Local Plans in water-stressed areas.
Both figures are on the table — and this month the water industry came out publicly in favour of changing them.
What’s actually proposed
Defra’s review of water efficiency standards in the Building Regulations 2010 put forward three changes:
- Cutting the minimum Water Efficiency Standard from 125 l/p/d to 105 l/p/d
- Cutting the optional technical standard from 110 l/p/d to 100 l/p/d, for areas of water stress or other local need
- Revising the water calculator and the fittings-based approach, to reflect how water use and fitting technology have moved on since the standard was written
There’s also a call for evidence attached, looking at whether rainwater harvesting and grey/black water reuse should play a bigger role in future.
The driver is blunt, and it isn’t really about the environment: water scarcity has become a housing supply problem. Defra’s own consultation puts it in cash terms — failing to manage water demand could mean over 61,000 homes not being built this parliamentary term, at a cost of some £25 billion. Cambridge and parts of Sussex have already seen schemes held up because demand outstripped supply. Twenty litres per person per day, multiplied across a site, is the difference between a scheme that fits inside the water resource envelope and one that stalls.
Where it stands right now
The consultation opened on 23 September 2025 and closed on 16 December 2025. Defra has not yet published its response, so nothing in Approved Document G has changed: 125 l/p/d remains the standard you design and calculate to today, with 110 l/p/d where a Local Plan policy or planning condition requires it.
The stated intention is to implement the Part G changes during 2026, subject to the consultation outcome and parliamentary approval, followed by a six-month transitional period (CIH briefing, September 2025).
The news this month is Water UK — the industry’s trade association — publishing its response backing the 105 l/p/d figure. It also supports the fittings-based route to demonstrating compliance as simpler and more consistent, and argues for a single national standard rather than a patchwork of locally set numbers (Water Magazine, 3 August 2026). If ministers agree, that last point would be a quiet relief to anyone who’s had to work out which of three water policies a particular district council is currently applying.
Water UK’s caveat is worth noting too: tighter new-build standards alone won’t deliver the demand reductions England needs — retrofit, smart metering and more efficient appliances have to do the heavy lifting on the existing stock. Useful context for how this is likely to be framed when the response lands.
What it means in practice
The jump from 125 to 105 isn’t enormous, but it’s enough to bite on schemes that currently scrape through. If you’ve been passing at 118 or 120 with a fairly standard fittings spec, that margin disappears.
The pressure lands where it always does: shower flow rate, bath capacity, WC flush volumes, and basin and kitchen tap flow rates. A generous bath and a 9 l/min shower head will eat the new headroom between them without any help. The other lever is rainwater or greywater reuse, which the calculator already recognises — and which the call for evidence suggests the government is interested in leaning on harder in future.
There’s a compliance angle too. The consultation notes that actual consumption in some new homes runs as high as 195 l/p/d — either because people use water in unexpected ways, or because dwellings aren’t being built to the standard on the drawings. Expect more attention on whether the fittings that were specified are the fittings that got installed.
What we’d suggest doing
Don’t redesign anything yet. Do know your number.
Run your standard house types through the calculation and see which ones would still pass at 105. One dwelling type covers every identical plot on a site, so this is a small piece of work that tells you a lot about your exposure — and it’s far cheaper to fix a specification on a spec sheet than after a Building Control inspection.
WaterMonkey does exactly that: the full official water efficiency methodology, with live PASS/FAIL as you type at 125 or 110 l/p/d, rainwater and greywater included, free in your browser. Building Control-ready PDF reports are £25 +VAT, and one dwelling type covers every identical plot on the site — so a whole estate needn’t cost the earth. We’ll update the calculator as soon as the revised standard and methodology are confirmed.
If you’ve got a site where water is already the sticking point — or a planning condition asking for something tighter than 110 — get in touch and we’ll tell you how we’d sort it.
Sources: Review of Water Efficiency Standards in the Building Regulations 2010 — Defra consultation · Water UK backs tougher water efficiency standards for new homes — Water Magazine, 3 August 2026 · CIH briefing on Defra’s Part G consultation