Who is responsible for preparing a system before chlorination?

The system owner, employer or other duty holder remains responsible for ensuring that the water system is properly prepared and that suitable competent assistance is appointed. The water hygiene provider is responsible for specifying and carrying out the technical preparation agreed in the method statement, but appointment of a contractor does not transfer the duty holder’s overall responsibility for managing the risk.

Before work starts, the duty holder should provide accurate information about the installation, its use, previous incidents, known defects and any vulnerable users who may be affected. They should also arrange access to plant rooms, tanks, outlets, valves and other relevant parts of the system, and coordinate the work with building occupants, facilities teams and other contractors. Any permit-to-work, isolation or notification requirements should be agreed before chlorination begins.

The competent provider should then translate that information into a practical preparation plan. This normally involves reviewing available drawings and records, tracing the system where necessary and confirming how water enters, circulates through and leaves the installation. The provider should establish which outlets, branches, storage vessels, calorifiers, pumps, hoses, filters and other components are included, excluded or require separate treatment.

Preparation may include:

• checking that valves, drain points and dosing points are accessible and operate correctly;
• isolating connected equipment or sections that could be damaged by the treatment;
• removing or managing items such as point-of-use filters, carbon filters and treatment equipment where they could consume chlorine or become contaminated;
• cleaning storage tanks and removing sediment, scale, biofilm or other deposits that could prevent disinfectant contacting the surfaces;
• opening representative outlets and flushing sections so stagnant or heavily contaminated water is not left in the installation;
• identifying dead legs, low-use branches, redundant pipework and other areas where disinfectant may not circulate;
• checking that materials, seals, pumps and connected components are suitable for the proposed chemical concentration and contact period; and
• providing safe drainage arrangements for chlorinated water and preventing its uncontrolled discharge.

The division of work should be recorded rather than assumed. For example, the duty holder may arrange access, isolation of unrelated services, removal of stored goods and notification of affected occupants, while the specialist contractor undertakes technical flushing, tank cleaning, dosing and post-treatment checks. If defects prevent effective preparation, the provider should report them and explain whether they need to be corrected before disinfection or dealt with as a limitation of the work.

Preparation is complete only when the provider can demonstrate that the intended treatment is practicable. This should be confirmed through suitable checks, such as verifying flow at outlets, confirming that the system can be drained, inspecting tanks and establishing that all relevant sections can receive disinfectant. Where a system cannot be fully prepared, the limitation, affected area and resulting risk should be documented, with remedial action recommended.

A clear record should identify who completed each task, what was found, which parts of the system were treated and any areas left outside the scope. The chlorination report should then be capable of being read alongside the risk assessment, method statement, chemical records, flushing results and water testing evidence. This creates an auditable connection between preparation and the conclusion that disinfection was suitable.

Blue Fish Water Management Ltd can advise duty holders on the preparation requirements for commercial, industrial and domestic water systems, including the practical steps needed before chlorination and the records needed to support water safety compliance. The important principle is that preparation is shared operationally but retained as a management responsibility by the system owner or duty holder.