4. Preventing or controlling the risk
You should first consider whether you can prevent the risk of legionella by looking at the type of water system you need. For example, identify whether it is possible to replace a wet cooling tower with a dry air-cooled system.
The key point is to design, maintain and operate your water services under conditions that prevent or adequately control the growth and multiplication of legionella.
Cleaning and disinfecting your water system
It is important to maintain the cleanliness of your water system. The mechanisms and frequency for doing this will depend on the system you have and whether cleaning or disinfecting is being done routinely or because of a problem identified during monitoring.
The frequency and method of routine cleaning and disinfecting should be identified within your risk assessment. This will take account of factors such as:
- whether the system is open or closed
- the type and level of contamination
- the people that could be exposed
Cleaning a cooling tower pack
When you can easily remove a cooling tower pack and reinstate it safely without damage, this will help you inspect it and assess the need for cleaning. However, you should consider the tower’s construction and the possibility of removing it when deciding how to clean and maintain the water system.
Whether the pack is removed or not, you should:
- demonstrate evidence of its cleanliness
- make an assessment using appropriate techniques
- record any findings recorded
You can find more guidance on cooling tower packs in Part 1 of Legionnaires' disease: Technical guidance.
Describing the controls you need
If you identify a risk that you are unable to prevent, you must introduce a course of action. This is called a ‘written control scheme’ and it will help you manage the risk from legionella and implement effective control measures, by describing:
- your system, for example by developing a schematic diagram
- who is responsible for carrying out the assessment and managing its implementation
- the safe and correct operation of your system
- what control methods and other precautions you will be using
- what checks will be carried out, and how often will they be carried out, to ensure the controls remain effective
You should:
- ensure that the release of water spray is properly controlled
- avoid water temperatures and conditions that favour the growth of legionella and other micro-organisms
- ensure water cannot stagnate anywhere in the system by keeping pipe lengths as short as possible or removing redundant pipework
- avoid materials that encourage the growth of legionella (the Water Fittings and Materials Directory references fittings, materials, and appliances approved for use on the UK Water Supply System by the Water Regulations Advisory Scheme)
- keep the system and the water in it clean
- treat water to either control the growth of legionella (and other microorganisms) or limit their ability to grow
- monitor any control measures applied
- keep records of these and other actions taken, such as maintenance or repair work