- Group A and Group B apply to Regulation 9 monitoring.
- Nine parameters are Group A in every Regulation 9 supply.
- Other parameters can become Group A due to source or treatment circumstances.
- Group B covers the remaining regulated parameters not already sampled under Group A.
Group A purpose
DWI says Group A monitoring checks core compliance, organoleptic and microbiological quality, and treatment effectiveness.
Always-Group-A parameters
Coliform bacteria, colony counts 22°C, colour, conductivity, E. coli, pH, odour, taste and turbidity are Group A in all Regulation 9 supplies.
Conditional Group A parameters
Some parameters become Group A when particular treatment chemicals are used or where the source has characteristics that make the parameter relevant.
Group B purpose
Group B checks the other standards and indicator parameters and, where relevant, disinfection by-products.
Frequency and variation
Frequency depends on supply volume. The Regulations allow variation for some parameters under conditions, but E. coli cannot simply be removed from monitoring.
Practical checklist
- Keep the local authority monitoring schedule.
- Record whether each sample is Group A, Group B or investigative.
- Attach the requested parameter list and full result.
Frequently asked questions
Does Group B mean “less important”?
No. The groups organise the monitoring programme; Group B is not a list of optional or unimportant parameters.
Do small domestic Regulation 10 supplies use Group A and B?
No. The Group A/B framework described here is for Regulation 9 monitoring.
Keep the records behind this work together.
Use the free tools or start a 7-day trial to see how sampling, maintenance, actions and documents can sit in one source-to-tap record.
- DWI: What sampling is required?
- DWI: Regulation 9 commercial and public supplies
- DWI: Regulation 7 monitoring
Regulatory guidance can change. Check the current DWI material and your local authority for the position applying to your supply.