What is a safe temperature for the hot water heater?

We have all heard of the advice to "lower the temperature of your hot water heater to save money." Perhaps you've read it online or maybe a friend or family member advised you. But my wife recently brought up the idea that it could be dangerous to do this for your health. While you may no longer scold you from burning hot water, you may get some bacterial or fungal infection due to an increased growth in the now warm (no longer killer), wet, dark tank that is your hot water heater.  So I determined it was my job to find the truth!

The answer to is it safe for you to lower the temperature is - it depends.  Below is information from the European Guidelines, OSHA, and Shriners Burn Institute to help inform & guide you.

It appears to me that at 60ºC (140ºF), everything is killed off rather quickly and is generally recommended by everyone, however, you risk getting burned in under 5 seconds.  Even OSHA can't make up their mind on what to recommend as you'll see below; so the question remains what will I do?

120-125ºF. This temperature wont scald us and we don't have a weakened immune system that would make us prone to falling ill easily. This temperature is also recommended for when you have children to help protect them. (Random side note: Temperatures of 60ºC or higher cause gradual erosion of glassware in a dishwasher.) Also, at 125ºF, while it may not kill bacteria, it likely wont encourage bacterial growth, which is good enough for me since the cold water will still likely have bacteria in it anyway. Lastly, temperatures above 60ºC encourage limescale deposits and since we live where the hardest water in the country is, I try to prevent it as best as I can. However, I do use the water booster on the dishwasher so that the dish detergent works at its optimal temperature.

So my question to you is, what temperature do you have yours set to?  After reading this, do you plan on changing it to a higher or a lower temperature?

Two more additional random side notes: From energysavers.gov "For each 10ºF reduction in water temperature, you can save between 3%–5% in energy costs." and even our own power company recommends that we keep the water heater tank at 120ºF.

Caution:Below is for the nerds like me who want to know everything.

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Here are some facts that you should know about water, burns, and the human skin from Shriners Burn Institute:

Likewise, the most dangerous bacteria mentioned (or that I could find) in regards to water heater is the Legionella. The name came about from an outbreak in July of 1976 from a hotel where there was a convention from the American Legion when this mysterious disease made 221 people sick and caused 34 deaths. 

Here are the facts about Legionella (USA suffers from between 10,000 and 50,000 cases each year, mostly being sporadic cases not associate with outbreaks) and how temperature affects it and the typical water heater colored in yellow and typed in bold font:

Temperature range	Effect on Legionella
70 - 80ºC (158-176ºF)	Disinfection range
66ºC (151ºF)	Legionella will die in 2 minutes
60ºC (140ºF)	Legionella will die in 32 minutes
55ºC (131ºF)	Legionella will die in 5 to 6 hours
50 to 55ºC (122-131ºF)	Legionella can survive but do not multiply
20 to 50ºC (68 - 122ºF)	Legionella growth range
35 to 46ºC (95 - 115ºF)	Legionella ideal growth range
Below 20ºC (68ºF)	Legionella can survive but are dormant

Likewise for other bacteria in general from the foodsafetysite:

74ºC (165°F)	Most bacteria die; some spore-forming bacteria survive.
60ºC (140°F)	No bacteria growth; some survive.
59ºC (139°F)	Danger Zone.
52ºC (125°F)	Some bacterial growth; many survive
37ºC (98.6°F)	Body temperature - Greatest bacterial growth and toxin production by some.

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This is what European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease (page 54) has to say on the matter:

It is recommended that hot water should be stored at 60°C and distributed such that a temperature of at least 50°C and preferably 55°C is achieved within one minute at outlets. Care is needed to avoid much higher temperatures because of the risk of scalding.

OSHA or the Occupational Safety & Health Administration also has two important pieces about the disease:

Q. Can Legionnaires' disease be prevented?  

A. Yes. Avoiding water conditions that allow the organism to grow to high levels is the best means of prevention. Specific preventive steps include:

• Regularly maintain and clean cooling towers and evaporative condensers to prevent growth of LDB. This should include twice-yearly cleaning and periodic use of chlorine or other effective biocide.
• Maintain domestic water heaters at 60°C (140°F). The temperature of the water should be 50°C (122°F) or higher at the faucet.
• Avoid conditions that allow water to stagnate. Large water-storage tanks exposed to sunlight can produce warm conditions favorable to high levels of LDB. Frequent flushing of unused water lines will help alleviate stagnation.

Q. Do you recommend that I operate my home water heater at 60°C (140°F)?  

A. Probably not if you have small children or infirm elderly persons who could be at serious risk of being scalded by the hot water. However, if you have people living with you who are at high risk of contracting the disease, then operating the water heater at a minimum temperature of 60°C (140°F) is probably a good idea. Consider installing a scald-prevention device.