How to Treat Water With Bleach or Tablets

Plain-language steps for disinfecting clear water with unscented household bleach or purification tablets, and why you must confirm amounts officially.

When you cannot boil water, chemical disinfection is a backup option. Two common tools are plain household bleach and purification tablets. Both can work well, but the amounts matter, and getting them wrong either leaves germs alive or makes the water unpleasant and potentially unsafe.

Because of that, this page explains the process and the rules, and then sends you to the official source for the exact amounts. Please confirm the dose on the official page before you rely on it.

Which bleach to use

The US EPA and Ready.gov guidance is specific. Use regular, unscented liquid household bleach that contains 5 to 9 percent sodium hypochlorite as its only active ingredient. Check the label.

• Do not use scented bleach, colour-safe bleach, splash-less formulas or bleach with added cleaners.
• Do not use bleach with a concentration outside the range on the label guidance.
• Old bleach loses strength over time, so use a bottle that is within its date and has been stored away from heat and sunlight.

The number of drops you add depends on the strength printed on the label and the volume of water. The EPA publishes a table for this. Look up your bottle's strength and your water volume there rather than guessing. In Canada, check the guidance on the Government of Canada power outage page linked below, since concentrations and wording can differ.

The steps for bleach

1. Start with clear water. If it is cloudy, let it settle and strain it through a clean cloth or coffee filter first, as described in our guide on purifying water in an emergency.
2. Use a clean container and measure the volume of water carefully.
3. Add the number of drops from the official table for your bleach strength. Use a clean, dedicated dropper, not one that has touched anything else.
4. Stir or shake the container well.
5. Let it stand for 30 minutes.
6. The water should have a slight chlorine smell. Official guidance says that if it does not, repeat the dose once and let it stand for another 15 minutes before drinking.

If the water smells strongly of chlorine, you can pour it back and forth between clean containers, or let it stand uncovered for a few hours, to improve the taste.

Using purification tablets

Tablets are convenient because the dose is pre-measured. The rules are simple:

• Follow the label exactly, including the water volume per tablet and the contact time. Some products need 30 minutes, and others need much longer, particularly for cold or cloudy water.
• Check the expiry date. Keep the bottle sealed and away from heat and moisture.
• Do not use more or less than the label states.
• Cold water slows the process, so read the label for temperature notes.

Different tablets use different chemicals, and some are not suitable for everyone, such as people who have certain health conditions or are pregnant. If this applies to you, ask a pharmacist or doctor, or choose another method.

What chemicals do not do

Bleach and tablets treat germs. They do not remove fuel, pesticides, heavy metals, salt or other chemicals. They are also less reliable on cloudy water, which is why clearing it first matters. If officials say water is chemically contaminated, use bottled water instead.

Other safety points

Label every treated container with the date and what you did. Treated water should be kept in a clean, covered container and used within a reasonable time. For longer storage tips, read best water storage containers and how long stored water lasts.

If you are shopping for gear, browse our water hub. And whichever method you pick, read the current official page before an emergency, not during one.

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