Mechanical
Domestic water services design
Domestic water services design with calculated demand, sized storage and generation, and legionella risk designed out at layout stage.
- Discipline
- Mechanical
WHAT IT IS
Water services design covers the supply of wholesome cold water and the generation and distribution of hot water: incoming supply, storage, generation, pipe sizing, and the controls that keep temperatures where they need to be.
Temperature control is a safety requirement, not a comfort one. Cold water below 20 °C and hot water stored at 60 °C and distributed to reach 50 °C within a minute at the outlet are the ACOP L8 control measures, and the layout either makes them achievable or it does not.
WHEN YOU NEED IT
On any new building, any extension that adds sanitary provision, and any refurbishment of an existing water system — particularly where the building has had a legionella risk assessment that identified design issues rather than maintenance ones.
DELIVERABLES
What you receive
- Loading unit demand calculation
- Cold water storage sizing
- Hot water generation and storage sizing
- Pipe sizing calculations
- Water services drawings and schematics
- Temperature control and monitoring requirements
STANDARDS
Standards applied
The editions in force at the time of design. Where a standard is amended mid-project we confirm which edition the appointment is based on.
- BS 8558:2015Design, installation, testing and maintenance of services supplying water for domestic useBSI
- BS EN 806Installations inside buildings conveying water for human consumptionBSI
- CIBSE Guide GPublic Health and Plumbing EngineeringCIBSE
- HSG274 Part 2Control of legionella bacteria in hot and cold water systemsHSE
- ACOP L8Control of legionella bacteria in water systemsHSE
QUESTIONS
Common questions
What temperatures must hot and cold water systems achieve?
Under ACOP L8 and HSG274 Part 2, cold water should be stored and distributed below 20 °C, hot water stored at 60 °C or above, and hot water should reach 50 °C at the outlet within one minute of running. These are control measures against legionella and are designed for rather than managed afterwards.
How do you design out legionella risk?
By removing the conditions legionella needs at layout stage: no dead legs or blind ends, storage sized to turn over rather than stagnate, branch runs kept short so outlet temperatures are reached quickly, and materials selected that do not support microbial growth. Design decisions are far cheaper than lifetime management.