Hot Water Safety and Water Efficiency Requirements

What This Requirement Covers

Approved Document G addresses sanitation, hot water supply, and water efficiency. It requires that hot water systems are installed safely (to prevent scalding and the growth of Legionella bacteria) and that new dwellings meet water efficiency targets.

Key Requirements

Hot Water Safety (G3)

1. Hot water must be stored at a minimum of 60 degrees Celsius and distributed at a minimum of 55 degrees Celsius to prevent Legionella bacteria growth
2. However, water delivered to baths must be limited to a maximum of 48 degrees Celsius by a thermostatic mixing valve (TMV) or other temperature-limiting device
3. The requirement for bath temperature limiting applies to all new dwellings and care homes
4. Unvented hot water systems (pressurised cylinders) must be installed by a competent person (G3 registered) and must comply with BS EN 12897
5. Safety devices (temperature and pressure relief valves, expansion vessel) must be installed and the discharge pipe must be visible and run to a safe location

Water Efficiency (G2)

1. New dwellings must achieve a maximum water consumption of 125 litres per person per day (calculated using the Water Efficiency Calculator)
2. Where imposed by planning conditions (optional requirement), the target is 110 litres per person per day
3. The water efficiency calculation considers:

- WC flush volume (dual flush: 4/2.6 litres is common) - Basin, bath, and shower flow rates - Washing machine and dishwasher consumption - Tap flow rates

1. Flow restrictors, aerators, and low-flush WCs are common measures to achieve the targets

Sanitary Facilities (G1, G4, G5, G6)

1. Every dwelling must have at least one WC, one washbasin, and one bath or shower
2. WCs must discharge to a foul water drainage system
3. Washbasins must be provided in or adjacent to every WC
4. Where food is prepared, a sink with a supply of hot and cold water must be provided

Practical Compliance Tips

1. Install thermostatic mixing valves on baths in all new dwellings; this is a mandatory requirement to prevent scalding
2. Ensure hot water is stored at 60 degrees C to prevent Legionella; do not set the cylinder thermostat lower to save energy
3. Unvented hot water systems must be installed by a G3 qualified installer; Building Control will ask for the installer's credentials
4. Run the water efficiency calculator during the design stage to select compliant appliances and fixtures
5. Low-flow showers and taps can significantly reduce water consumption; specify products with flow rates that meet the target
6. Ensure the temperature and pressure relief valve discharge pipe is visible (typically terminating outside at low level) so that operation can be observed
7. Keep the G3 installation certificate and commissioning record for Building Control sign-off