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? Here's a guide to properly diluting bleach so you can use it as a disinfectant. Spoiler: a lot of you are doing it wrong.
Why dilute bleach?
If you want to disinfect a surface with bleach, diluting bleach with water is actually more effective than using it straight. Diluted bleach is also gentler on the materials that the bleach contacts, and saves money and trouble—a bottle of bleach can last a very long time when you're only using a few tablespoons at a time.
Use cold or room temperature water
When washing things with soap, we usually go with warm or hot water, since heat energy helps chemical molecules to interact with each other more often. If you've ever washed dishes with cold water at a campsite, compared to the hot water of your sink at home, you already know this difference.
But when it comes to sanitizing with bleach, the higher temperature isn't worth the drawbacks. 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 minimize 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 okay, 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.
Use the right kind of bleach
You'll find a lot of things that market themselves as "bleach," like color-safe bleach, splashless bleach, Clorox-branded cleaning solutions, and more. When we're talking about using bleach to disinfect things, that refers to regular household bleach (like this) with an active ingredient of 8.25% sodium hypochlorite. For the dilution instructions below, the CDC says to use bleach that is anywhere between 5-9% sodium hypochlorite. If it doesn't give a percentage, don't use it. And if the percentage is outside that 5-9% range, either don't use it or look up the appropriate dilution ratio from the manufacturer or another source.
Mix the bleach and water in the correct ratio
Don't just dump a glug of bleach into a bucket of water. Measure. The CDC recommends the following ratios, using standard household bleach:
5 tablespoons per gallon of room temperature water, or
4 teaspoons per quart of room temperature water
Note the difference in units: if you're measuring by the gallon, you're using five tablespoons. That's a little more than a quarter-cup. (If you've heard that you should use 1/3 of a cup per gallon of water, that's basically the same as this rule. Close enough.)
On the other hand, for a quart, that means four teaspoons. If you're mixing up a smaller amount for a spray bottle, two teaspoons will work for 16 ounces. This is easy math if you've memorized common kitchen units—three teaspoons to a tablespoon, four tablespoons to a quarter-cup, two cups to a pint, two pints to a quart, four quarts to a gallon. I understand that not everybody has committed these to memory, so here is a handy chart from Clorox that lays out the appropriate measurements for buckets and spray bottles of various sizes.
Store it properly
Diluted bleach doesn't last forever. If you're mixing it in a bucket right before you use it, and dumping any leftovers down the drain immediately, you don't need to worry about storage. But if you're mixing a supply to use throughout the day, as in a spray bottle, dump it at the end of the day.
Bleach breaks down once it's diluted, and the solution is only good for about 24 hours. That same spray bottle isn't going to be effective for sanitizing the day after tomorrow. Bleach solutions also break down faster in sunlight, so if you will be storing the solution temporarily, use an opaque container.