The Part G water-use limit for new dwellings, why fittings drive it, why saving hot water saves twice, and the 48 °C bath limit.
Approved Document G gives separate anchors for water efficiency and for hot-water safety, two different aims that learners often blur together. Remember which is which: 125 or 110 litres is water efficiency, 48 °C is scald safety.
Water efficiency: litres per person per day
Part G controls how much water a new home is expected to use. The requirement is written as a limit on litres per person per day, calculated from the fittings that are installed rather than measured once people move in.
The normal new-dwelling limit is 125 litres per person per day. Where the optional requirement is imposed, for example through a planning condition, the tighter figure is 110 litres per person per day.
The water-efficiency methodology adds up the assumed use of each type of fitting: WCs, taps, showers, baths, washing machines, dishwashers and any water softener or outdoor supply. Because the result depends on the fittings, the practical way to pass is to specify efficient ones: lower-flow taps and showers, dual-flush or low-volume WCs, and appropriately sized baths, all chosen so the totalled figure stays under the limit.
This is a design-stage requirement, so it sits alongside, not instead of, the day-to-day water-fittings rules that keep water wholesome. The exact numbers and the calculation method are set out in the current Part G, so confirm them there.
Flow limiters and self-closing taps
A flow limiter changes the litres delivered per minute while the tap is open. For example, at the same supply conditions, a 20-second wash uses 2 litres at 6 litres/minute but 1 litre at 3 litres/minute. A self-closing tap saves water in a different way: it ends the running time. Neither device changes the volume needed to fill a basin to the same level; slower filling simply takes longer.
Hot water and leaks: the other side of efficiency
Reducing how much hot water a household draws saves twice: once as metered water, and again as the fuel or electricity that would have heated it, so it also cuts the number of times the cylinder has to reheat. This is why water-efficiency advice pays as much attention to hot outlets, such as showers and hot taps, as to cold ones.
A dripping tap or a small leak wastes water continuously, day and night, until it is fixed, so prompt repair is as much a part of water efficiency as choosing low-flow fittings.
Hot-water safety at a bath
In a new dwelling in England, hot water supplied to a fixed bath is limited to a maximum of 48 °C. A suitable blending valve or other appropriate temperature-limiting device can provide that control. The cylinder’s hygiene regime remains a separate requirement. The 48 °C ceiling is not suitable for every bather: where vulnerable users are at risk during whole-body immersion, water must not exceed 44 °C and may need to be cooler.
Keep these as Building Regulations revision facts. They do not replace the full document, local building-control advice, manufacturer instructions or practical assessment requirements.