Many new homes in England must be designed to use no more than 110 litres of water per person per day. That figure is demonstrated through the government's water efficiency calculator, and it is one of the most common conditions attached to residential planning permissions. The good news: passing it is largely a matter of specifying the right fittings early. This guide explains how the calculator works, which flow rates get you there, and where it sits in your sustainability statement.
The 110 litres per person per day (l/p/d) standard is the optional, tighter water-efficiency requirement under Part G of the Building Regulations. Local planning authorities apply it through local plan policy — and in London it is effectively standard. If you are unsure whether your scheme needs to address it, our guide to what a sustainability statement is sets out the wider picture.
The two ways to comply: fittings or calculator
Approved Document G offers two routes to demonstrate water efficiency:
- The fittings approach — a simplified table of maximum flow rates and capacities. Meet every fitting limit and you comply, no calculation needed. This route targets the baseline 125 l/p/d standard.
- The water efficiency calculator — the methodology in Approved Document G that adds up the consumption of each fitting to produce a single litres-per-person-per-day figure. This is the route used to demonstrate the tighter 110 l/p/d optional standard that planning conditions usually require.
For the 110 l/p/d target, you will almost always be using the calculator. It converts each fitting's flow rate or volume into a daily consumption figure using fixed use factors, sums them, adds a fixed allowance for outdoor use, and divides by an assumed occupancy.
The fittings and flow rates that pass 110 l/p/d
Hitting 110 l/p/d is achievable with widely available, sensibly specified fittings. Typical specifications that get a standard dwelling under the limit include:
- WC: dual-flush 4/2.6 litres, or 4.5/3 litres (average effective flush is what the calculator counts).
- Taps (basin): around 5 litres per minute, using flow restrictors or aerators.
- Kitchen tap: around 6 litres per minute (kitchen taps are often left a little higher for practicality).
- Shower: around 8 litres per minute — the shower is usually the single biggest lever in the calculation.
- Bath: a smaller nominal capacity (for example 180 litres to overflow) helps, as baths carry weight in the sum.
- Dishwasher and washing machine: water-efficient appliances count where specified.
The shower flow rate is the number to watch. Because showers are assumed to be used daily and for several minutes, shaving a litre or two per minute off the shower often makes the difference between passing and failing. Where a design includes multiple bathrooms or a generous bath, the other fittings simply need to be tighter to compensate.
How the calculator is presented in a sustainability statement
For a residential scheme, the water efficiency calculation is a core component of the sustainability statement. A robust statement will:
- state the applicable standard (110 l/p/d) and the policy that requires it;
- list the specified fittings with their flow rates and capacities;
- show the calculator output confirming the figure is at or below 110 l/p/d; and
- commit to the specification via a condition-ready schedule so it survives to construction.
Water efficiency sits alongside the statement's other themes — energy, biodiversity net gain and urban greening — but it is distinct from the carbon and heating measures that belong in your energy statement. Keeping the two documents in their lanes avoids duplication and confusion for the case officer.
Why 110 litres matters — and where it is tightening
The 110 l/p/d standard exists because much of England is classified as seriously water-stressed. Reducing per-person demand in new homes eases pressure on supply, defers costly new infrastructure and cuts the energy used to treat and pump water. Some authorities in the driest regions now push beyond 110 l/p/d towards even lower targets, and a growing number encourage rainwater harvesting or greywater reuse to bank additional headroom in the calculation. Designing to a comfortable margin below 110 — rather than exactly on the line — is the safest approach, because it leaves room for a client to upgrade a shower or add a bath later without breaching the condition.
Common mistakes to avoid
- Specifying a powerful shower for marketing appeal, then failing the calculator by a wide margin.
- Leaving fittings "to be confirmed" — the calculator needs actual flow rates, not placeholders.
- Confusing the 125 l/p/d fittings route with the 110 l/p/d calculator route.
- Forgetting that the specification usually becomes a planning condition — the fittings installed must match the ones calculated.
For how water efficiency fits alongside biodiversity and greening on a constrained plot, see our guide to delivering 10% biodiversity net gain on a small site.
How Fortress Associates can help
Fortress Associates produces automated sustainability statements for planning applications across every UK local authority. Each report is free and covers energy, water efficiency (including the 110 l/p/d water calculator), 10% biodiversity net gain under the Environment Act 2021, urban greening and BREEAM where required — and, for London sites, the Urban Greening Factor under London Plan Policy G5. Start on our sustainability statement page or get in touch through our contact page.
Sources & further reading
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