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Legionella – everything you need to know about water temperatures
Posted 3rd January 2019

Legionella – everything you need to know about water temperatures

Employers right across the UK should be aware of Legionella and the potential risk to employees if the water supply to buildings, factories or warehouses is not monitored regularly.

Do you know what temperatures your water systems should be running at – find out below:

 

What temperatures should my water systems be?

In all buildings, healthcare or non-healthcare sites cold water temperatures should be below 20°C within two minutes of opening the outlet. Stored water temperatures in tanks should also be below 20°C.

Hot water temperatures are a bit more complicated. In a non-healthcare building, hot water should be dispensed from an outlet at 50°C within one minute. If you have a large hot water heater (Calorifier), this should always operate above 60°C, if your hot water system is circulating, the return line should also be above 50°C.

In healthcare sites, this is slightly different. The Calorifier flow and return temperatures should both be the same as in a non-healthcare building, but hot water should reach any outlet at 55°C.

Not all water heaters are bound by the 60°C rule though, point of use water heaters (small water heaters with less than 15L in volume) and combination storage water heaters (water heaters with an internal cold-water storage tank on top of the unit) only need to operate between 50-60°C. (55°C in healthcare).

 

What outlet points need temperature measurements?

Sentinel outlets should be monitored monthly, and a representative selection of other outlets on a rotational basis over a defined period.

What does this mean for you and your business?

Sentinels are those outlets which are closest and furthest from a source of water. You can have sentinels for different types of water you have on site, so mains water sentinels, tanked water sentinels (if you have cold water storage tanks) and hot water sentinels. You might think that you would have two sentinels for each, closest and furthest, but this is not necessarily the case, it depends how your water systems are laid out.

 

What about representative outlets, what outlets need to be covered, and over what ‘defined period’?  

Industry standards state that you should check the temperatures of all of your non-sentinel outlets over the course of a year, assessing around 10% of your non-sentinel taps each month, so that all are covered by the end of the year.

You should also check the operating temperature and return temperatures (if they have return lines) of your calorifiers every month. The guidance also says you should check subordinate loop temperatures quarterly. This is generally only applicable in larger buildings. A subordinate loop is a separate hot water circulating loop that branches off from the main circulating system.

If you have a larger building to consider, you should check your pipework schematics to see if you have any subordinate loops present.

 

How often do temperatures need monitoring?

  • Most temperatures need checking monthly. You should check your sentinels, Calorifier flow & return and some of your representative outlets every month.
  • Subordinate loops should be checked quarterly.
  • Cold water storage tanks should have temperatures checked annually, in the middle of summer.

 

What type of thermometer should be used? 

The only specific requirement is that the thermometer must be calibrated. Your thermometer should be calibrated every year, if your thermometer has not been calibrated, the temperatures taken using it cannot be used as evidence in court, and that is what your log book is there for, it’s your due diligence defence if the worst should happen. 

You should also use a thermometer that is suitable for the task. If you have a Calorifier you need to record flow and return temperatures from, or outlets fitted with TMVs (thermostatic mixing valves), you will need a thermometer with a contact probe, so you can take pipework readings.

 

What is the correct way of taking a temperature reading?

This depends where you are taking the temperature from, they all vary slightly: 

  1. When taking the temperature from a cold tap you should immerse the probe under the stream of water. You should leave the water to run for two minutes and record the temperature.
    If the temperature levels off before two minutes, or ‘stabilises’, you can record the temperature at that time. You don’t need to wait the full two minutes if the temperature stops changing.
  1. When taking the temperature from a hot tap without a TMV you should immerse the probe under the stream of water. You should leave the water to run for a minute and record the temperature. If the temperature levels off before the one minute is up, or ‘stabilises’, you can record the temperature at that time. You don’t need to wait the full minute if the temperature stops changing.
  1. When taking the temperature from a hot tap with a TMV you should run the tap and push the contact probe thermometer to a piece of uninsulated, unpainted pipework prior to the TMV. If using an infrared thermometer, put a piece of black matt tape on the hot pipe before the TMV and direct the beam onto that.
    You should leave the water to run for one minute and record the temperature. If the temperature levels off before the minute, or ‘stabilises’, you can record the temperature at that time. You don’t need to wait the full minute if the temperature stops changing.
  1. When taking the flow temperature from a Calorifier you should push the contact thermometer to a piece of uninsulated and unpainted pipework. If using an infrared thermometer, put a piece of black matt tape onto the pipe. Hold the probe there until the temperature stabilises and record. When taking the return temperature, follow the procedure for checking the flow, but try to take the temperature from the return pipe before the circulation pump, as these can generate a lot of heat which can artificially raise the return temperature.
  1. When taking the temperatures from a cold-water storage tank you should first immerse the probe in the stored water within the tank, ideally as far from the inlet valve as possible. Record this temperature, then run the inlet valve and immerse the probe under the stream of water. Record the temperature after 2 minutes or after the temperature stabilises, which ever happens first. You should check the temperatures this way round, as running the inlet valve for two minutes can drop the stored water temperature in the tank, particularly in smaller tanks.

 

What action should be taken if the temperature is not in the ideal range?

This is where it gets complicated! This depends greatly on the temperature you are taking, if its from a tank, the mains, if it’s hot and by how much the temperature is out by.

Within guidance it is recommended that you should consider carrying out weekly legionella sampling until temperatures are back within range, however there are other options depending on your situation.

Your organisation must have procedures in place to follow in the event of out of specification temperatures, typically these will involve informing the responsible person, but you should see what your procedures recommend. If you are unsure what to do, it is best to get specialist help from the likes of our team here at Euro Environmental.

 

What records of temperatures should I keep and for how long?

Read our blog on temperature monitoring and recording here.

 

What is a Legionella Risk assessments and when do they need to be carried out?

Regular monitoring of your water system(s) is paramount. If someone has contracted Legionnaires, it can spread to others as it is very contagious. See how often and when Legionella risk assessments are required here.

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