Source-backed values from Approved Document G for new dwellings and fixed baths.
Approved Document G is useful for source-backed value recall because it gives separate anchors for water efficiency and for hot-water safety — two different aims that learners often blur together.
Water efficiency. For a new dwelling the normal limit is 125 litres per person per day, worked out with the water-efficiency methodology from the fittings specified — WCs, taps, showers, baths and any water softener or outdoor supply. Where the optional requirement is imposed through planning, the tighter figure is 110 litres per person per day, which usually means choosing lower-consumption fittings.
Hot-water safety at a bath. Part G limits the hot water delivered to a fixed bath to a maximum of 48 °C. Because a cylinder or combi stores and delivers water far hotter than that, the limit is met by blending — typically an in-line thermostatic mixing valve on the bath supply — not by turning the whole system down. The aim is scald protection, and it matters most for young children, older people and anyone with reduced sensation or mobility.
Keep these as Building Regulations revision facts, and remember which is which: 125 or 110 litres is water efficiency, 48 °C is scald safety. They do not replace the full document, local building-control advice, manufacturer instructions or practical assessment requirements.