Heating water to kill any bacteria etc

[Keitai]

Just put my hot water on for first time in months. I heard there's a bacteria or virus which gets killed at 70 degrees. Is it best after all this time to leave heater on for as long as possible to kill the bug?

I usually only put it on for 15 mins to get it warm enough to wash dishes etc that wouldn't kill it

 

[pcaouolte]

The bacteria that you are thinking of is Legionella. in order to kill it you need to heat the water to at least 60 degrees C. The water coming out of your hot taps should also be at least 50 degrees C when the tap has been running for one minute. At 60 degrees C 90% of the legionella bacteria will die within 2 minutes.

There is a thermostat under the metal cover over the immersion heater at the top of your tank (the bit that is labelled BACKER). THERE ARE ALSO LIVE WIRES UNDER THAT COVER. Switch off the electricity, undo the nut on the cover, lift of the cover and check that the thermostat is set to 60 degrees (it will adjust with a screwdriver).

You can check the temperature at the taps by holding a thermometer under the running hot water for one minute.

 

[Friday round]

Hi @pcaouolte Really good info. Just a question when testing at the tap. Should all taps need to reach 50C so test the furthest, or is this just a secondary test of the cylinder’s water temp?

 

[JohnD]

The bacteria that you are thinking of is Legionella. in order to kill it you need to heat the water to at least 60 degrees C.

That is not true.


However, persistently heating the cylinder for short periods so it is only warm is the worst thing OP can do.

 

[pcaouolte]

That is not true.

Perhaps you can help the OP by providing him with the true information?

 

[JohnD]

Legionella does not grow at temperatures above 45C or below 20C

If it is stored in a cylinder, it will not grow above 45C and will be killed at 50C or above. So heating it quickly, and storing it hot, ready for use, will do all that is needed.

Keeping it lukewarm is the worst possible choice. There is no need to have dangerously scalding water in an ordinary domestic home.

 

[Hugh Jaleak]

It is recommended to set a thermostat for Domestic Hot water to 60-65ºC to prevent Legionella bacteria developing. https://www.hse.gov.uk/legionnaires...r systems should be,one minute at the outlets.

 

[Madrab]

Water @ 50deg will take at least 2-3 hours to kill the bacteria to a level (~10%) where it's unlikely to cause harm .... running the HW up to 60 deg will kill the same level of bacteria (~10%) in 2 minutes, hence why it is recommended to have stored HW @ 60Deg.

It also allows the HW to reach the outlet @ around 50Deg, again another HSE recommendation (55deg for medical)

Scalding is another issue and why the TMV2/3 standards were brought in.

Certainly agree though that keeping HW lukewarm is not a safe way to store HW.

 

[Friday round]

Should all taps need to be able to reach 50C, so test the furthest, or is this just a secondary test of the cylinder’s water temp?

 

[JohnD]

Water @ 50deg will take at least 2-3 hours to kill the bacteria to a level (~10%) where it's unlikely to cause harm ....

And I keep my (heavily insulated) cylinder hot all day

Since the fresh water entering it is too cold to support growth, there's no reason to suppose it will be teeming with bacteria anyway.

 

[Madrab]

Since the fresh water entering it is too cold to support growth, there's no reason to suppose it will be teeming with bacteria anyway.

No, but all incoming mains water does have dormant bacteria, which when it hits the optimum temperature, will start to multiply quickly. All cylinders have a temperature gradient where the top of the cylinder will be hottest and the bottom the coolest, hence the 60deg recommended setting to ensure the majority of the cylinder reaches above 50Deg.

If the stat was say set to 50Deg then the water below the stat will always be cooler, potentially within the range where the bacteria can multiply.

 

[Keitai]

I normally heat it for an hour (i just press the one hour button once no timer settings so i use as and when) but could click for another hour which should make it reach 70 degrees which I think it's set at. A lot of electricity though. I haven't heated the water for four months, over the summer.

 

[CBW]

A lot of electricity though. I haven't heated the water for four months, over the summer.

Leaving it sat for 4 months without heating can be bad too. Did you run any of the hot taps regardless of heating it? Have you considered a different method of heating your water?

 

[Keitai]

Yeah ran the water despite being cold. I guess leaving stagnant not good.

 

[Harry Bloomfield]

My gas heated hot water system includes a once per week option to raise the cylinder to 60C, for the purpose of killing off the Legionella, the rest of the time the stored water can be stored at a cooler programmed temperature. 55C is suggested to be adequate to kill Legionella. So I would suggest the OP uses a similar regime of heating the water to 60C at least once per week, for safety.

I like my hot water good and hot, so I have it set for 60C all of the time.