Why You Should Never Dilute Bleach With Hot Water

Photo: Shutterstock
Photo: Shutterstock

Bleach makes a great disinfectant, but safety is important. You already know not to mix it with ammonia, vinegar, or alcohol, but did you know that the temperature of the water also matters?

The CDC and others recommend mixing 1/3 of a cup of bleach per 4L of room temperature water. Using hot water isn’t dangerous, like some other things people are doing with bleach (please don’t put it on your skin), but it has some distinct disadvantages.

First, a steamy hot bleach solution is more likely to allow some of the bleach to waft into the air. Bleach fumes can irritate your eyes and nose, and you should be using bleach in a well ventilated place if possible, anyway. Using room temperature water will minimise this effect.

The other problem is that hot water will make the chemicals in bleach break down more quickly. Even a properly made bleach solution will be less effective if you leave it out overnight, which is why you should mix up a fresh solution every day. If you need a bucket of diluted bleach to last for an afternoon’s cleaning spree, it will keep its effectiveness better with lukewarm water than with hot.

There is one situation where hot water is ok, though, and that’s laundry. Clorox says it’s fine to wash your clothes in hot bleachy water, and the heat can even help the bleach work more quickly. The concerns about fumes and about waning effectiveness don’t apply when the bleach is confined to the inside of the washing machine for the short amount of time it takes to wash your socks.

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