What should a potable water chlorination report include?

A potable water chlorination report is the formal record that demonstrates how a drinking water installation was verified following disinfection. A properly prepared report should allow an independent reader to identify the asset concerned, understand the evidence obtained, confirm how the findings were evaluated and determine whether the system can be put into service.

It should normally contain the following information:

• Client and site details: the client’s name, site address, relevant building or system identification, and the person who authorised the work.
• Report reference and dates: a unique document number, the date of the work, the date of sampling, the date of issue and, where relevant, the date of any follow-up visit.
• System identification: a clear description of the installation or section treated, including any areas excluded from the work. Drawings, schematics or marked-up plans can help show the boundaries of the system.
• Responsible personnel: the names and roles of the person carrying out the chlorination, the person taking samples and the person reviewing or approving the report.
• Applicable criteria: the standard, specification, project requirement or client acceptance criteria used to assess the work. The report should make clear whether the assessment relates to a new installation, alterations, recommissioning or remedial disinfection.
• Equipment and chemicals: the relevant equipment used, the chemical identity and, where necessary, its concentration or batch information. Equipment used for measurement should be identifiable and supported by current calibration or verification records.
• Operational restrictions: any precautions needed while the work was undertaken, including isolation arrangements, notices, access restrictions or measures used to prevent treated water entering an occupied or live supply.
• Sampling plan: the locations selected, the reason for their selection, the sequence of sampling and whether samples represent outlets, storage tanks, branches or other parts of the installation. Sample points should be sufficiently identifiable for later comparison.
• Laboratory documentation: the laboratory name, sample references, receipt details, analytical methods and the status of the laboratory’s relevant accreditation where laboratory analysis has been used. The report should include the laboratory certificates or attach them as controlled appendices rather than relying only on a summary table.
• Quality and traceability records: sample container details, preservation and transport information where applicable, sampler identification, and any chain-of-custody documentation. These records help establish that the reported result relates to the correct installation and sampling event.
• Exceptions and limitations: inaccessible outlets, parts of the system not treated, unusual operating conditions, interrupted work, missing records or other factors that could affect the reliability or scope of the conclusion.
• Corrective actions: a description of any issue identified, the action recommended or completed, the person responsible and whether further verification is required. Open actions should not be hidden within general commentary.
• Conclusion and authorisation: a concise statement of the outcome against the stated criteria, together with the name, role and signature or approved electronic authorisation of the person responsible for the technical review.

The report should distinguish between facts recorded at the site and conclusions drawn from those facts. For example, a measurement, a laboratory result and an assessment against a specified acceptance criterion are separate pieces of information. Keeping them separate makes the report easier to audit and reduces the risk of an unexplained pass or fail decision.

Results should also be presented with the units, sampling point and date clearly shown. If a result is outside the required criterion, the report should explain whether the system was rejected, restricted from use, treated again or subject to additional investigation. A conclusion that simply says “satisfactory” provides less useful evidence than a conclusion linked to defined criteria and supporting records.

Where a report is issued for a construction or refurbishment project, it should be capable of being read alongside the relevant drawings, commissioning records and handover documents. Where the work relates to an existing building, the report should identify the operational context and any parts of the installation that could not be assessed. This is particularly important where shared supplies, storage arrangements or complex distribution networks make the treated boundary difficult to establish.

A chlorination report is not, by itself, a substitute for a legionella risk assessment, a water safety plan or ongoing monitoring arrangements. It records a specific disinfection and verification activity. The client should therefore retain it with other water hygiene and building-services records, so that later maintenance, investigations or regulatory reviews can be informed by the original evidence.

Before accepting the document, a client should check that the system boundary is unambiguous, all supporting certificates are present, the sample references match the stated locations, the criteria are identified and any unresolved restrictions or actions are visible. If those elements are missing, the report may confirm that work was attempted but may not provide sufficient evidence that the potable water system was suitable for use.