110 vs 125 litres: which Part G water target applies?
Every new home in England has to meet a water efficiency limit. Here is how to tell whether yours is the standard 125 litre requirement or the tighter 110 litre one.
At a glance
Part G of the Building Regulations limits how much wholesome water a new dwelling is expected to use. The figure is expressed in litres per person per day and is worked out using the water efficiency calculation in Appendix A of Approved Document G. There are two limits, and which one applies depends on your planning permission.
The standard requirement: 125 litres per person per day
Regulation 36(2)(a) sets a limit of 125 litres per person per day. It applies to every new dwelling, and to dwellings formed by a material change of use, such as a barn conversion or an office converted into flats. If nothing in your planning permission says otherwise, this is the target you design to.
The optional requirement: 110 litres per person per day
Regulation 36(2)(b) is the optional requirement of 110 litres per person per day. It only applies when it has been imposed as a condition of planning permission. Local planning authorities in water-stressed areas commonly add it, and it is increasingly standard wording in decision notices.
What about Wales?
Wales has its own Approved Document G, and its standard requirement for new dwellings is already 110 litres per person per day. If the site is in Wales, design to 110 litres.
How much harder is 110 litres?
The difference is about 15 litres per person per day, and the shower is usually where it is won or lost. Using the Appendix A method, a typical three-bedroom house with a dual-flush 6/4 litre WC, 6 L/min basin taps, 8 L/min kitchen taps, a 10 L/min shower and no bath comes out at about 117.1 litres. That passes 125 but fails 110.
| Change from that specification | New result | 110 target |
|---|---|---|
| None (shower 10 L/min) | 117.1 L | Fail |
| Shower reduced to 8 L/min | 106.9 L | Pass |
| Shower 8 L/min and WC 4/2.6 L | 100.5 L | Pass |
Your own fittings will give different figures, which is why it is worth running the calculation before the specification is fixed.
Does the target change the report?
The method is the same for both targets. The report states which requirement was selected and shows the calculated figure against it. Make sure you select the right one: a report showing 125 litres will not discharge a planning condition that asks for 110.
Frequently asked questions
Does the 110 litre requirement apply to every new home?
No. In England the 110 litres per person per day limit only applies where a planning condition imposes the optional requirement. If your planning permission has no such condition, the standard 125 litre limit applies.
Is the calculation different for the 110 litre target?
No. The Approved Document G Appendix A method is exactly the same. Only the limit the result is compared against changes, so you can test both targets with the same specification.
What fittings usually meet 110 litres?
Most homes that pass 110 litres have a shower of around 8 litres per minute or less and a low-flush dual-flush WC, with aerated basin taps. Every specification is different, so run the calculation before ordering fittings.
Check your property against either target
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