The water heater is one of the biggest energy-consuming appliances in most homes, so if you’re looking for a place to cut back on energy costs, it’s a good place to start. But before you dial back your water heater’s thermostat a few degrees, there are a few things to think about.

Set the temperature too low, and you could turn your water heater into a breeding ground for dangerous bacteria. Set it too high, and you could be setting yourself up for a scalding accident.

How Low Can You Go?

The short answer: 120 degrees Fahrenheit. This is the preset thermostat temperature in most new water heaters, and it’s the recommended setting of the U.S. Department of Energy.

At this temperature, harmful pathogens like the kind that cause Legionnaires’ disease are prevented from multiplying and may be killed. As the temperature gets higher, pathogens die off quicker. For that reason, other agencies like the Occupational Safety and Health Administration (OSHA) recommend a water heater temperature of 140 degrees Fahrenheit.

If everyone in your home has a strong immune system, 120 degrees should be considered safe, but it’s also the minimum. It’s safer to choose a temperature closer to 140 degrees, especially if anyone in the home has a compromised immune system. You might also need to set the temperature higher if you have a dishwasher that doesn’t generate its own heat.

What About Scalding?

At 140 degrees, water can cause a third degree burn in five seconds. And because it takes several seconds for hot water to travel through your pipes and reach your faucet or showerhead, you’ll never know exactly when the scalding water will suddenly arrive.

Children can be more susceptible to water burns because their skin is thinner than that of adults, and the elderly may also be at increased risk due to reduced sensitivity, mobility and reaction time.

In the tug-of-war between pathogenic safety and scalding safety, there is a solution: anti-scald valves. By installing these at each point of contact with hot water, you can keep your water heater set to 140 degrees while making sure it never gets hotter than 120 degrees at the tap. Installing an anti-scald valve may be a DIY project for an experienced amateur plumber, but the complexity of the job varies by the layout of the plumbing. Be sure to call a licensed plumber if you have a tricky installation.

But What About Energy Efficiency?

Saving energy and money is important, but it’s not as important as saving yourself and your family from harmful illnesses. That said, it’s possible to cut costs without using your water heater’s thermostat to do it:

• Use less hot water. Take shorter showers and favor the dishwasher over hand-washing, which usually uses more water.
• Insulate your hot water heater and pipes. There are easy-to-install pieces of insulation that are pre-cut for these purposes, so this may be an afternoon DIY project.
• Replace your water heater. The average water heater lasts 8 to 12 years, and that’s if it’s properly maintained. Water heaters that are older or overdue for maintenance could be far less efficient than they were on day one.