How to Prevent Legionella in Hot Water Cylinders

Legionella remains relatively uncommon in the UK, however when incidents do occur, the finger of blame is often pointed at bacteria in stored water. The risk of bacteria developing within a storage device will be largely dependent on 4 key factors

1.    The Movement of the Water Water that is stagnant for a prolonged period of time can be a breeding ground for bacteria such as legionella, which is why the correct sizing of a cylinder is a key element of any project.

The focus of most specifications is to ensure the user has hot water on demand, however specifying cylinders which are too big for a particular application can result in stagnating water. In commercial applications, a circulating “de-stratification” pump can be fitted to ensure even temperatures throughout the cylinder.

2.    The Temperature of the Water The critical temperature in which Legionella can become a real danger is between 20°C and 45°C. This is due to the fact that Legionella bacteria remains dormant below 20°C, does not multiply above 50°C and is killed off above 55°C.

Whilst most hot water cylinders will be set to ensure the water temperature remains higher than 60°C, inefficient cylinders and renewable energy applications can often be subject to lower temperatures.

3.    The Efficiency of the Cylinder It is vital the hot water cylinder is regularly maintained to ensure that all connections are clear and water is flowing freely and to the required pressure.  Stagnant water or lower temperatures can all increase the chances of bacteria forming in the cylinder.

4.    The Material Used in the Cylinder Tests showed that after 7 days of immersion in water, 80% of stainless steel and 90% of plastics were coated in a biofilm, where bacteria begins to form.

Copper’s natural ability to kill 99.9% of bacteria such as Legionella , MRSA and ecoli within 2 hours enables clients to protect the well being of the patients, children and employees from this potentially life threatening disease. Similarly, the concentration of E. coli when tested after the 7 days was 100 times lower on the copper than the stainless steel or plastic.

In tests, it took 34 days for E. coli 0157 to die on stainless steel, 4 days on brass and just 4 hours on copper.

In summary, the risk of Legionella can be minimised by taking the following actions:

  • keep the system clean
  • keep the water moving
  • keep the water below 20°C or above  55°C
  • specify copper hot water cylinders

Click here to download a copy of our "How to prevent Legionella in Hot Water Cylinders" guide

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