People who hand-wash a lot of dishes often wonder whether hot water kills germs. Others want to know if hot water kills germs in the laundry. And some people want to save a little money and use cold water for both dishwashing and laundry. Does anyone have it right? Yes and no. Hot water is capable of killing some germs, but the real question is, how hot must the water be, and for how long do the germs have to be exposed to it?
Too Hot for Hand-Washing
While it is possible to kill some bacteria with hot water alone, the water has to be at a temperature well above what your skin can tolerate. Most people can tolerate a temperature of 110 degrees for a short time, but that's about it.
Specific water temperatures for killing germs are difficult to pinpoint, but drinking water provides a good reference. To sanitize water for drinking, the Environmental Protection Agency (EPA) recommends boiling the water for at least 1 minute, at altitudes up to 5,000 feet. At higher elevations, water should be boiled for 3 minutes. So that's 212 degrees F (at sea level) to reliably kill bacteria and pathogens to make water potable. By contrast, most dish and clothes washing are done at temperatures lower than 120 degrees (which is the maximum water heater temperature recommended by the U.S. Consumer Product Safety Commission), so it's not safe to assume you're killing a lot of germs with the hot water.
Hot Water Does Aid Cleaning
Even if hot water doesn't kill much bacteria, it does help to get your dishes and clothes cleaner, thus ridding them of potential hosts for bacteria. Hot water and detergent together attack oils and grime. That oil and grime that you rinse away with the water contains bacteria or could otherwise host bacteria. Without hot water, the detergent is less effective, and oily dishes and clothes don't get as clean.
How to Sanitize Dishes and Clothes
Since it's not feasible to sanitize your dishes or clothes with boiling water, you have to use a disinfectant. With laundry, you can wash the clothes and disinfect at the same time, using an appropriate disinfecting detergent for the wash cycle. To sanitize dishes, you must wash the dishes first, then soak them in a sanitizing solution to kill bacteria. The easiest reliable method to sanitize dishes is to use chlorine bleach:
1. Prepare a solution of 2 teaspoons household bleach per gallon of water in a clean sink or washing tub.
2. Wash the dishes thoroughly with hot water and your favorite dish detergent, then rinse. Be sure to do this in a separate sink basin or washing tub from the bleach solution.
3. Soak the washed dishes in the bleach solution for at least 2 minutes. The dishes must be submerged.
4. Lift each dish out and drain it into the sink, then air-dry it on a clean dish rack.
Do not use a bleach solution with aluminum, iron, plain steel (non-stainless), or enameled cookware with chips or exposed metal. Bleach accelerates rust.
There are very good reasons why you must wash the dishes first and air-dry them. Washing the dishes removes food and oils that would reduce the effectiveness of the bleach solution. Air-drying prevents cross-contamination from drying multiple dishes with the same towel (and towels are common hosts for bacteria).
Making Water Safe in an Emergency. Centers For Disease Control and Prevention.
Michaels B, Gangar V, Schultz A et al. Water temperature as a factor in handwashing efficacy. Food Service Technology. 2002;2(3):139-149. doi:10.1046/j.1471-5740.2002.00043.x
Emergency Disinfection of Drinking Water. United States Environmental Protection Agency.
Avoiding Tap Water Scalds. U.S. Consumer Product Safety Commission.
4 Steps to Food Safety. U.S. Department of Health & Human Services.