- There is no single standard “private water supply test” that suits every supply or every reason for sampling.
- Regulation 9 supplies in England use Group A and Group B monitoring, with additional parameters where the risk assessment requires them.
- Regulation 10 supplies do not use Group A and Group B: the routine minimum is a different five-parameter set, except for the single-dwelling provisions.
- A laboratory result is a snapshot of the water at the sampled point and time; it does not replace risk assessment, treatment maintenance or investigation of known hazards.
1. There is no single private water test
When somebody asks for a “private water supply test”, the first question is why is the water being tested? A local-authority regulatory sample, an investigation after a failure, a treatment check and a voluntary domestic screening package can all contain different parameters.
For regulatory monitoring in England, the required panel is driven by the type of supply and the findings of the risk assessment. The Drinking Water Inspectorate (DWI) separates Regulation 9 monitoring into Group A and Group B. Regulation 10 supplies use a different monitoring set, while Regulation 8 private distribution systems are monitored on a risk-assessment basis.
2. Regulation 9 Group A
Regulation 9 covers private supplies used as part of a commercial or public activity and supplies that meet the Regulation 9 volume criteria. For these supplies, local authorities carry out both Group A and Group B monitoring, plus any extra monitoring required by the risk assessment.
DWI identifies nine parameters that are Group A in every Regulation 9 supply in England:
- coliform bacteria;
- colony counts at 22°C;
- colour;
- conductivity;
- Escherichia coli (E. coli);
- hydrogen ion concentration (pH);
- odour;
- taste; and
- turbidity.
These parameters give information about microbiological quality, appearance and acceptability, and aspects of treatment performance. They are not a complete description of every possible chemical or microbiological hazard.
If you need the detailed purpose, frequency and classification rules, use the dedicated Group A vs Group B monitoring guide. This page is concerned with what may be inside the test panel rather than reproducing the full monitoring schedule.
3. Conditional Group A parameters
Some parameters become Group A only in specified circumstances. DWI's current England guidance identifies the following examples:
| Parameter | When it can be Group A in England |
|---|---|
| Aluminium | Where it is used as a treatment chemical, or where the water originates from or is influenced by surface waters. |
| Iron | Where it is used as a treatment chemical, or where the water originates from or is influenced by surface waters. |
| Manganese | Where the water originates from or is influenced by surface waters. |
| Ammonium, nitrate and nitrite | Where chloramination is practised. |
The key point is that the same chemical can sit in a different part of the monitoring programme depending on the circumstances. Do not infer the scope of a sample from the words “Group A” without seeing the actual requested parameter list.
4. Regulation 9 Group B
Group B is the broader Regulation 9 monitoring suite. DWI describes its purpose as checking compliance with the remaining standards and indicator parameters in Schedule 1 that are not already being monitored as Group A, and checking relevant disinfection by-products where disinfection is used.
Depending on the supply and the applicable monitoring programme, this broader chemical work can include parameters such as nitrate, metals, pesticides and disinfection by-products. It should not be reduced to a generic “chemistry test”: the important evidence is the actual parameter schedule and the result for each parameter.
England's amended Regulations allow local authorities, under specified conditions, to reduce the monitoring frequency for certain parameters or cease monitoring them. E. coli cannot be reduced or ceased under those provisions. The risk assessment can also justify higher-frequency or additional monitoring. That is another reason why two Regulation 9 supplies may not have identical laboratory schedules.
5. Regulation 10 testing
Regulation 10 applies to smaller non-commercial private supplies in England that do not fall into Regulation 9. These supplies do not use Group A and Group B monitoring.
For Regulation 10 supplies other than a supply serving a single dwelling only, DWI states that the local authority must monitor at least every five years for:
- conductivity;
- Enterococci;
- E. coli;
- pH; and
- turbidity.
The local authority must increase monitoring where the risk assessment shows this is necessary, and can include other Schedule 1 parameters or other parameters where a risk to human health is identified.
A single dwelling used exclusively for domestic purposes has a different position. Routine monitoring is not mandatory unless the owner or occupier asks the local authority to do it, although the authority can monitor at its discretion where there is concern. DWI says that when testing is requested, the same five parameters above are normally tested as a minimum, with additional tests where risk indicates them.
See the dedicated Regulation 10 guide for the classification, risk-assessment and five-year-cycle detail.
6. Regulation 8 testing
Regulation 8 concerns private distribution systems: water supplied by a water company and then distributed privately beyond the point of supply. DWI states that monitoring for these systems should be based on the regulatory risk assessment, so there is no single fixed Group A/Group B panel for every Regulation 8 system.
Depending on the hazards identified, the monitoring may include microbiology, pH, conductivity and turbidity, metals arising from pipework or fittings, taste and odour, and disinfection by-products where relevant. The point is to test the hazards that the private distribution system could introduce or worsen.
If your supply starts with mains water but is distributed through private tanks or pipework, see the Regulation 8 private distribution systems guide rather than assuming the source is a Regulation 9 or 10 private abstraction.
7. Risk-based and investigative testing
Regulatory groups are only part of the picture. A risk assessment can identify additional hazards that justify extra testing. Examples might include a contaminant associated with local geology, a pesticide risk in the catchment, a metal associated with pipework, or a treatment-related parameter.
Investigative sampling after a poor result or operational incident may also use a deliberately narrower or different panel. For example, an investigation into recurring microbiological failures may need a different sampling plan from an investigation into discolouration, nitrate or corrosion. The panel should follow the question being investigated rather than simply repeating a generic package.
Keep the reason for the sample with the result: regulatory Group A, regulatory Group B, Regulation 10, additional risk-assessment parameter, investigation or operational check. The same numeric result can be interpreted very differently when the reason and sample point are missing.
8. What the main parameter types tell you
| Parameter type | Examples you may see | What it helps assess |
|---|---|---|
| Microbiological | E. coli, coliform bacteria, Enterococci, colony counts | Evidence of faecal contamination, general microbiological condition or changes that may need investigation, depending on the parameter and supply type. |
| Physical / indicator | Turbidity, colour, conductivity, pH | Changes in water character, treatment conditions, source influence or acceptability. These results can also provide context for other hazards. |
| Organoleptic | Taste and odour | Whether the water has abnormal or unacceptable sensory characteristics and whether a change may need investigation. |
| Chemical | Nitrate, metals, pesticides and other Schedule 1 parameters | Compliance with chemical standards and source-, catchment- or plumbing-related hazards selected by the monitoring programme. |
| Treatment-related | Parameters connected with treatment chemicals or disinfection by-products | Whether treatment is introducing a parameter that needs monitoring or whether by-products need to be controlled without compromising disinfection. |
This is an orientation, not a substitute for the laboratory schedule. If you already have a result and need help understanding units, qualifiers, reporting limits and flags, use How to Read a Private Water Supply Laboratory Report.
9. Sample point and accreditation
What is tested is only half of the sampling question. Where and how the sample is taken matters. DWI's Regulation 12 guidance says a regulatory sample is normally taken at the tap used to supply water for human consumption, usually the kitchen tap, or another representative point appropriate to the premises and purpose.
For regulatory monitoring, sampling, transport and analysis must meet the required accredited standards. DWI states that drinking-water sampling, transport and analysis carried out under the Regulations should be within the relevant UKAS accreditation arrangements. A home test kit or an unaccredited sample can still have a limited screening use, but it should not be represented as equivalent to the regulatory process.
Sample handling can also affect results. Microbiology bottles, preservation, timing, temperature and sampling technique are controlled for a reason. If you are arranging testing outside a local-authority programme, tell the laboratory what the result will be used for and ask it to confirm the required sampling and accreditation arrangements.
10. What one test does not prove
A satisfactory result is useful evidence about the water that was sampled, but it does not prove that the supply will remain satisfactory under every condition. DWI specifically warns that water quality can vary with seasonal source changes and treatment performance, and that a result at one point in time is not necessarily representative of all other times.
That is why private-supply management combines sampling with source-to-tap risk assessment, treatment operation and maintenance, inspection of the supply, and follow-up of defects or abnormal results. A “pass” on a small panel also cannot say anything about a parameter that was never tested.
11. Records to keep
Do not keep only the front page of a laboratory certificate or a message saying that the water “passed”. Preserve enough evidence for somebody else to reconstruct the sampling event later.
- the sampling instruction, laboratory quotation or local-authority schedule showing the requested parameters;
- the date and time of sampling;
- the exact sample point and premises;
- the purpose of the sample and, where relevant, its Group A, Group B, Regulation 10, risk-based or investigative reason;
- the sampler or sampling organisation where shown;
- the complete original laboratory report, including units, methods, qualifiers and accreditation information;
- any advice received about abnormal results;
- corrective actions, repeat or investigative sampling and the outcome; and
- links to the risk assessment, treatment or maintenance event that explains why the sample was taken.
The dedicated sampling records guide covers the evidence trail in more detail.
12. Practical checklist
- Confirm the supply classification before assuming which regulatory panel applies.
- Ask for the actual parameter list, not just the name of a testing package.
- Check whether the sample is regulatory, investigative, risk-based or operational.
- Confirm the sample point and who is responsible for taking the sample.
- For regulatory work, confirm the appropriate accredited sampling, transport and laboratory arrangements.
- Keep the complete report and parameter schedule together.
- Do not interpret “not tested” as “safe” or “compliant”.
- Link abnormal results to advice, investigation and corrective action.
- Use trends over time where they are meaningful, but remember that sampling is still a snapshot.
13. Frequently asked questions
Does every private water supply test include the same parameters?
No. The parameter list depends on the supply type, the regulatory monitoring programme, the risk assessment and the reason for sampling. A Regulation 9 Group A sample, a Regulation 10 sample and an investigative sample can legitimately contain different parameters.
What parameters are always in Regulation 9 Group A monitoring in England?
DWI lists nine parameters in all Regulation 9 Group A programmes in England: coliform bacteria, colony counts at 22°C, colour, conductivity, E. coli, pH, odour, taste and turbidity. Other parameters become Group A only in specified circumstances.
Does a Regulation 10 private water supply use Group A and Group B?
No. DWI states that Regulation 10 supplies are not subject to Group A and Group B monitoring. For Regulation 10 supplies other than single dwellings, the specified routine set is conductivity, Enterococci, E. coli, pH and turbidity, with additional risk-based parameters where necessary.
Does every private water test include nitrate?
No. Nitrate is not one of the nine parameters that are always Group A for Regulation 9. It can be Group A where chloramination is practised and may otherwise form part of Group B or risk-based monitoring where applicable. Always check the actual parameter schedule.
Can I use a home water test kit instead of regulatory sampling?
A home kit may provide limited screening information, but it is not equivalent to regulatory sampling. DWI requires regulatory sampling, transport and analysis to meet specified accredited standards. If the result is needed for regulatory, enforcement or formal compliance purposes, use the appropriate local-authority and accredited arrangements.
Where is a regulatory private water supply sample normally taken?
DWI's Regulation 12 guidance says samples are taken from a point representative of water used for human consumption, usually the kitchen tap, although the correct point can differ according to the premises, treatment arrangement and purpose of the sample.
Does one satisfactory laboratory result prove the supply is safe all year?
No. A sample describes the water at a particular place and time and only for the parameters tested. DWI notes that source water and treatment performance can change with conditions and seasons, so sampling should be considered alongside the risk assessment, treatment operation, maintenance and any known hazards.
Keep the sampling context with the laboratory report.
Use the free tools or start a 7-day trial to keep sampling, maintenance, corrective actions and source documents in one supply record.
- DWI: What sampling is required?
- DWI: Regulation 7 monitoring
- DWI: Regulation 12 sampling and analysis
- DWI: Single dwelling supplies
- DWI: Private supply legislation
Regulatory guidance can change. Check current DWI material and your local authority for the position applying to your supply.