Who holds responsibility for chlorinating a drinking water system?

Responsibility for chlorinating a drinking water system is allocated according to who controls the premises, the water installation and the work being undertaken. The duty holder must ensure that any chlorination is properly planned, carried out by competent people, verified, and recorded before the system is returned to use.

The duty holder and the person carrying out the work have different responsibilities. An owner, landlord, employer, facilities manager or other organisation in control of a building may hold the primary duty for managing water safety. That organisation can use its own employees or appoint a specialist contractor, but appointing a contractor does not remove the need to select a competent provider, communicate relevant site information and check that the work has been completed satisfactorily.

Where several organisations share a building, responsibility should be defined in writing. For example, a building owner may control the incoming supply and main plant, while a tenant controls outlets within its occupied area. A managing agent may administer the premises, but the contract should make clear which party arranges remedial work, authorises system shutdowns, keeps records and manages the risks to occupants. Shared control requires cooperation rather than assumptions about who is responsible.

Construction and refurbishment projects require additional clarity. The principal contractor, plumbing contractor or commissioning engineer may be responsible for preparing and chlorinating newly installed or modified pipework as part of the project. The client or eventual system operator should still require evidence that the work meets the specified standard before accepting the installation. Handover information should identify the system boundaries, treatment undertaken, test results, outstanding defects and any restrictions on use.

A responsible organisation should normally ensure that the following matters are addressed before chlorination starts:

• the limits and configuration of the system are understood;
• the method statement identifies the chemical, concentration, contact period, flushing arrangements and discharge controls;
• risks to people, equipment and the environment have been assessed;
• users and affected contractors are informed about isolation, restricted access and possible interruption to the water supply;
• appropriate personal protective equipment and emergency arrangements are available; and
• the work is assigned to people with suitable knowledge, training and practical experience.

Chlorine is a hazardous substance, so the person arranging the work must consider exposure during chemical handling, dosing, sampling and flushing. This includes applying relevant control-of-substances requirements, preventing unauthorised access to treatment areas and ensuring that chlorinated water is discharged in a controlled manner. The responsible person should not rely solely on a contractor’s generic paperwork: the method must reflect the actual system, premises and surrounding drainage arrangements.

Verification is also part of the responsibility. A system should not be treated as successfully chlorinated merely because chemical has been introduced. The duty holder should obtain appropriate records showing the treatment performed and the results of residual chlorine, microbiological or other required testing. Where testing is outsourced, the organisation should confirm that the testing arrangement is suitable for the decision being made; UKAS-accredited water testing may be appropriate where reliable laboratory evidence is required.

Records should be retained with the water safety documentation. They may include the risk assessment, scope of work, method statement, chemical information, isolation plan, dates and times, sampling locations, analytical results, flushing records, certificates and details of any corrective action. These records allow the duty holder to demonstrate what was done and provide a baseline for future monitoring, investigation or recommissioning.

If results are unsatisfactory, responsibility remains with the duty holder to decide what happens next. Depending on the findings, this may involve additional flushing, repeat disinfection, investigation of dead legs or contamination sources, repair of defects, review of storage and distribution arrangements, or further sampling. A contractor can recommend and perform these measures, but the organisation controlling the system must ensure that the risks are addressed and that the system is not placed back into normal service prematurely.

For ongoing management, the responsible person should integrate chlorination records into the wider water safety plan and coordinate them with legionella risk management, maintenance and change-control procedures. Specialist water hygiene support can help with method statements, site coordination, sampling, UKAS-accredited testing and remedial recommendations, while the duty holder retains oversight of the system and its compliance arrangements.