What is a schematic diagram?

A schematic diagram is a simplified but accurate illustration of the layout of the water system, including parts temporarily out of use. While providing only an indication of the scale, it is an important tool as it allows any person who is not familiar with the system to understand quickly and easily their layout, without any specialised training or experience. These are not formal technical drawings but show what the systems comprise of, illustrating plant and equipment, including servicing and control valves, any components potentially relevant to the legionella risk, including outlets, strainers and filters or parts that are out of use.

There is nothing in law that prescribes a schematic diagram. However there is published guidance.

The Health and Safety Executive (HSE) Legionnaires’ disease Part 2: The control of legionella bacteria in hot and cold water systems provides guidance for dutyholders, which includes employers, those in control of premises and those with health and safety responsibilities for others, to help them comply with their legal duties.

The HSE guidance document makes 2 references to ‘schematic diagram’ and 1 reference to ‘schematic plan’. The references have been reproduced below and selected text made bold by the author of this blog to emphasise key points:

1. Introduction – Identify and assess sources of risk – In summary, the risk assessment should consider and evaluate description of the water system, including an up-to-date schematic diagram.

{Authors note: this guidance implies an up-to-date schematic diagram should be available for the risk assessments}

2. Appendix 2.1 – Legionella risk assessment – checklist gives the most common key requirements when assessing risk associated with a hot and cold water system based on mechanical, operational, chemical and management aspects: assessment of the validity of the schematic diagram which should include all parts of the system where water may be used or stored.

{Authors note: as above this guidance suggests a schematic diagram should be part of the risk assessments}

3. Appendix 2.2 – Legionella control scheme – summarise the information to include in a legionella written control scheme, i.e.: up-to-date schematic plan showing the layout of the system(s) and its location within and around the premises – this should identify piping routes, storage and header tanks, calorifiers and relevant items of plant, especially water softeners, filters, strainers, pumps and all water outlets.