Why do we have to clean shower heads?
When the HSE investigate cases of legionnaires’ disease, the majority are traced back to either showers or spa/hot tubs. That’s why, over 30 years ago, the HSE published the document called HSG70 which first set out technical guidance on how to manage the risk from legionella bacteria.
This document has since been replaced by L8 and HSG274 but the recommendations remain the same, ie every 3 months “Dismantle, clean and descale removable parts, heads, inserts and hoses (where fitted)”.
What makes showers such a high risk?
Legionella bacteria thrive in water when the temperature is between 20°- 45°C, since our preferred temperature of showers is ~40°C this is ideal for their growth.
Legionella bacteria like to live in biofilm and scale, it is these environments which provide the nutrients needed for continued growth.
For humans to contract legionnaires’ disease, we need to get the bacteria into our lungs. Showers emit a huge stream of water droplets, the smaller droplets (those that look like steam or fog) can be breathed in allowing legionella to enter our body. Our lungs also provide a great place for them to live, the temperature is usually 37/38°C which is perfect for their needs and we also provide them with a feast of nutrients.
How do we reduce the risk?
Legionella bacteria prefer stagnant conditions so the first line of defence is to make sure the showers are used regularly so that they are frequently flushed out of the system whilst their numbers are small. If you have an infrequently used shower, then either remove it or ensure it is flushed at least a couple of times each week. If either of these proves impractical, fit a “point of use” legionella filter to prevent the bacteria reaching the aerosol.
The next task is to remove their habitat and nutrient supply, this is done by descaling and disinfecting the shower head and hose. This task has to be repeated on a regular basis because both scale and biofilm formation are a continuous cycle. Specialist products are available which disinfect and descale in a single operation. For hand held showers you simply immerse the head and hose into a container of chemical or for fixed head showers (such as anti vandal, prisons etc) spray a slightly viscous chemical onto the showerhead.
For details and techniques on how to clean a shower, see the document Legionella Shower Head Disinfection & Descaling Techniques.