AES Sustainability Consultants
Based in Tiverton, Devon · Covers England, Scotland and Wales Accreditation stated by provider: ATTMA, SITMA, Elmhurst, ECMK, TrustMark, BREEAM, PassivhausOwn websiteUK-wide
02 · Building Regulations · Part G
Water efficiency calculations
Every new home in England must be designed so that water use is no more than 125 litres per person per day. A water efficiency calculation shows building control that the taps, toilets, showers, baths and appliances you have chosen meet that limit.
DWGuide by Dan Wallis · Updated 27 September 2026
This guide covers the rules in England. See Wales, Scotland and Northern Ireland.
Who needs oneAnyone building a new home or converting a building into homes
Who can do itUsually your SAP assessor or designer
WhenDesign stage, confirmed at completion if fittings change
56 providers listed across the UK
Featured (paid) listings first, then A–Z · How we check listings
Find providers by region
London (17) South East (8) East of England (10) South West (7) West Midlands (10) East Midlands (5) Yorkshire and the Humber (4) North West (8)
National providers (42)
Airtight Testing Staffordshire
Based in Stoke-on-Trent · Covers Staffordshire and UK-wide Accreditation stated by provider: ATTMAOwn websiteUK-wide
Apex Home and Energy Surveyors
Based in Warrington, Cheshire · Covers Warrington and WA postcodes for EPCs; calculation work across England and Wales Accreditation stated by provider: RICS, Elmhurst Energy, CHASOwn websiteUK-wide
Assessment Hive
Based in Goffs Oak, Hertfordshire · Covers London and throughout the UK Accreditation not yet checkedOwn websiteUK-wide
ATSPACE
Based in Royston, Hertfordshire · Covers England and Wales Accreditation stated by provider: Elmhurst, NHER, SITMA, TrustMark, Passivhaus Trust (Patron), BPEC, BSRIA, Passivhaus Trust PatronOwn websiteUK-wide
Base Energy
Based in Staines-upon-Thames, Surrey and Bootle, Merseyside · Covers UK-wide, including London Accreditation stated by provider: Elmhurst, CIBSE, TrustMark, BREEAMOwn websiteUK-wide
Briary Energy
Based in Hatfield, Hertfordshire · Covers UK-wide Accreditation not yet checkedOwn websiteUK-wide
Building Energy Experts
Based in Bristol · Covers Nationwide Accreditation stated by provider: Elmhurst, ATTMA, TrustMark, Retrofit Academy (Corporate Member), Retrofit Academy Corporate Member, AECBOwn websiteUK-wide
Complete EPC
Based in Finchley, London · Covers All of London, and elsewhere in the UK Accreditation stated by provider: Quidos, StromaOwn websiteUK-wide
Compliance 4 Buildings
Based in Hornchurch, Essex · Covers Nationwide (UK) Accreditation stated by provider: ATTMAOwn websiteUK-wide
Coventry Property Certification
Based in Coventry, West Midlands · Covers England and Wales Accreditation not yet checkedOwn websiteUK-wide
DAA Group
Based in London · Covers Nationwide across the UK Accreditation stated by provider: ATTMA, BPECOwn websiteUK-wide
E2 Specialist Consultants
Based in Birmingham office (head office Wakefield) · Covers Birmingham and 25+ West Midlands towns Accreditation stated by provider: SITMA, iATSOwn websiteUK-wide
Easy EPC Ltd
Based in Brighton, East Sussex · Covers Nationwide, with local landing pages for many UK towns including Leicester, Nuneaton and Coventry Accreditation not yet checkedOwn websiteUK-wide
Elmstead Energy Assessments & Building Services (EEABS)
Based in Colchester, Essex · Covers UK-wide, including London Plan energy assessments Accreditation stated by provider: Elmhurst, CIBSE Low Carbon Consultant, CIBSE Low Carbon Energy Assessor, EDSL TASOwn websiteUK-wide
Energist
Based in Cirencester, Gloucestershire · Covers Nationwide Accreditation stated by provider: Elmhurst, ATTMA, ANCOwn websiteUK-wide
Energy & Design
Based in Cannock, Staffordshire · Covers England, Scotland and Wales Accreditation stated by provider: Scotland Section 6 Approved Certifier of Design, BREEAM UK New Construction (Residential)Own websiteUK-wide
Energy Counsel
Based in Manchester, Greater Manchester · Covers Manchester, the North West and nationwide Accreditation stated by provider: CIBSE, BPEC, iATS, SITMA, BREEAM, AECB, ConstructionlineOwn websiteUK-wide
Energy National
Based in Rochdale, Greater Manchester · Covers Greater Manchester and East Lancashire locally; SAP work nationwide Accreditation stated by provider: Elmhurst Energy, Stroma, ABBE, BRE, TrustMarkOwn websiteUK-wide
Energycount
Based in Poole, Dorset · Covers Nationwide (UK) Accreditation not yet checkedOwn websiteUK-wide
Energytest
Based in Tunbridge Wells, Kent · Covers London and the South East; nationwide Accreditation stated by provider: ATTMAOwn websiteUK-wide
enevo
Based in Birstall, West Yorkshire · Covers UK-wide (national network of local assessors) Accreditation stated by provider: ATTMA, iATS, SITMA, Elmhurst, Stroma Certification, BREEAM, ABBEOwn websiteUK-wide
Environmental Economics
Based in Luton, Bedfordshire · Covers UK nationwide, including London Plan work Accreditation stated by provider: Elmhurst (overheating scheme)Own websiteUK-wide
EPC Assess Ltd
Based in Midlands · Covers Birmingham, Wolverhampton, Coventry and UK-wide Accreditation not yet checkedOwn websiteUK-wide
EPC Experts
Based in Coventry, West Midlands · Covers Coventry, Nuneaton, Rugby, Warwick and nationwide Accreditation not yet checkedOwn websiteUK-wide
Focus 360 Energy
Based in UK (several offices) · Covers Nationwide Accreditation stated by provider: Elmhurst, ECMK, StromaOwn websiteUK-wide
Gradwell Group
Based in Doncaster, South Yorkshire · Covers England-wide Accreditation not yet checkedOwn websiteUK-wide
HA Acoustics
Based in Harlow, Essex · Covers East Anglia, London, South West and nationwide Accreditation stated by provider: UKAS, iATSOwn websiteUK-wide
Manchester EPC Ltd
Based in Cheadle, Greater Manchester · Covers EPC visits within about 50 miles of Manchester; SAP and new-build work nationwide Accreditation not yet checkedOwn websiteUK-wide
Melin Energy Consultants
Based in Swansea · Covers UK-wide (offices in Swansea, Bristol and London) Accreditation stated by provider: Elmhurst (Approved Psi Value Competency Scheme), BREEAM AP, CIBSE, UK Thermography AssociationOwn websiteUK-wide
MES Building Solutions
Based in Newark, Nottinghamshire · Covers Throughout the UK (offices in Newark, London and Birmingham) Accreditation stated by provider: ATTMA, Elmhurst, AECB, TrustMarkOwn websiteUK-wide
MSAFE
Based in Bournemouth, Dorset · Covers Nationwide Accreditation stated by provider: UKAS (sound insulation testing)Own websiteUK-wide
PB Sustainability
Based in Wirral, Merseyside · Covers Nationwide Accreditation stated by provider: ABBE, CABE, ElmhurstOwn websiteUK-wide
Purple Energy Solutions
Based in UK (several offices) · Covers Nationwide Accreditation stated by provider: ATTMA, UKASOwn websiteUK-wide
QuinnRoss Energy
Based in Sittingbourne, Kent · Covers UK-wide, with a focus on Greater London and the South East Accreditation stated by provider: Elmhurst, UKAS, BRE Global, CIBSE Low Carbon Consultant, Low Carbon Energy AssessorOwn websiteUK-wide
sap2sbem
Based in Leek, Staffordshire · Covers UK-wide (desk-based) Accreditation stated by provider: ElmhurstOwn websiteUK-wide
SEES
Based in Durley, Southampton, Hampshire · Covers UK-wide Accreditation stated by provider: Elmhurst, ATTMA, BREEAM licensed assessor company, Stroma certifiedOwn websiteUK-wide
Southern Assessors
Based in Salisbury, Wiltshire · Covers UK-wide, with offices in London, Bristol and Birmingham Accreditation stated by provider: NHEROwn websiteUK-wide
Stroma Built Environment
Based in Wakefield, West Yorkshire · Covers UK-wide Accreditation stated by provider: UKAS (No. 2731), ATTMAOwn websiteUK-wide
UK Building Compliance
Based in Hinckley, Leicestershire · Covers UK-wide (England, Wales, Scotland and Northern Ireland) Accreditation stated by provider: ATTMA, Elmhurst, SITMA, BPEC, UKASOwn websiteUK-wide
Vision Energy & Sustainability
Based in Bollington, Cheshire · Covers UK-wide Accreditation not yet checkedOwn websiteUK-wide
Regional providers (check they cover your area) (2)
DATScotland
Based in Tealing, Dundee · Covers Scotland-wide Accreditation not yet checkedOwn website
UKSAPS
Based in Royston, Hertfordshire · Coverage not stated, so check with the provider Accreditation not yet checkedOwn website
The two limits
- 125 litres per person per day: the standard Part G requirement.
- 110 litres per person per day: the optional tighter requirement, which applies when your planning permission includes a condition requiring it. Check your decision notice.
How it is worked out
The calculation uses the flow rates and capacities of the fittings you plan to install. You can also use the "fittings approach", which sets maximum flow rates for each fitting. Changing fittings during the build can affect compliance, so tell your assessor if the specification changes.
In Wales, Scotland and Northern Ireland
This guide describes the rules in England. Building regulations are devolved, so here is how water efficiency calculations works in the rest of the UK.
Wales
Wales is stricter than England. 110 litres per person per day is the standard limit for every new home, not an optional extra. Homes created by conversion have a 125 litre limit.
Scotland
There is no per-person water calculation. Instead, new homes must use water-efficient fittings, such as toilets that use no more than 4.5 litres per flush and basin taps of no more than 6 litres a minute.
Northern Ireland
There is no water efficiency limit, so building control doesn’t need a water calculation.
Common questions
Does an extension need a water calculation?
No. The Part G water efficiency requirement applies to new homes.
What fittings make the biggest difference?
Toilets, showers and baths usually have the most effect. Dual-flush toilets and flow-restricted showers make the lower limits easier to meet.
What is the limit?
125 litres per person per day for a new home in England. A tighter limit of 110 litres applies when your planning permission includes a condition requiring it, so check your decision notice.
Who does the calculation, and when?
Usually your SAP assessor or designer, at design stage. It’s confirmed at completion if the fittings change, so tell your assessor about any changes to the specification.
New to the jargon? See our glossary of terms, from air permeability to TrustMark.