How to Make Water Safe at Home: Boiling, Bleach and Filters
Three ways to make water safe in an emergency: boiling, bleach or filtering. How many drops to use, how long to wait and what no method can fix.
A broken main, a flood or a notice from the authorities can leave your tap water in doubt overnight. If you have bottled water, use it. If you don't, you need to know how to make what you have safe, and there are three roads: boil it, disinfect it with bleach or filter it.
First, a warning the CDC repeats in every guide: if the water contains fuel, toxic chemicals or radioactive material, boiling, bleaching or filtering won't fix it. If it smells like gasoline or solvent, don't drink it and wait for instructions from the authorities.
Boiling: the safest option
If you can boil, boil. The CDC asks for a rolling boil for one minute, or three minutes above about 6,500 feet (2,000 meters). Let it cool and store it in clean, covered containers. Boiling kills bacteria, viruses and parasites, which the other two methods can't do on their own.
Boiled water tastes flat. Pouring it back and forth between two clean containers gives some of the taste back.
Bleach, when you can't boil
Use unscented household bleach (no perfumes or dyes) and check the label: the CDC table is for 5% to 9% sodium hypochlorite. Amounts for clear water:
| Amount of water | Drops of bleach |
|---|---|
| 1 quart (about 1 liter) | 2 |
| 1 gallon (3.8 liters) | 8 (a little under 1/8 teaspoon) |
| 5 gallons (a large jug) | 40 |
If the water is cloudy, double it. Stir well and wait at least 30 minutes before drinking. It should smell faintly of chlorine; if you can't tell, check the date and strength of your bleach.
Two precautions: never mix bleach with ammonia or other cleaners, and open a window when you handle it. And if your bleach has a different strength (1%, for example), the drops change, so check the full CDC table before improvising.
If you don't have bleach, the CDC accepts chlorine dioxide or iodine tablets, following the package directions.
Filters: useful, with fine print
This is the most common mix-up. According to the CDC, most portable filters do not remove bacteria or viruses; the ones that work on parasites say so on the label. That's why filtered water may need a second step, boiling or bleach, to be safe. A filter does help as a first pass with cloudy water, along with a clean cloth.
A minimal kit to keep at home
- A bottle of unscented bleach with the date visible, and a dropper.
- A pot you can boil in, and a way to heat it that doesn't depend on electricity.
- Water treatment tablets as a backup.
- Clean lidded containers for the treated water. Here is how to store and rotate your water.
If you're putting together your 72-hour kit, drop the bleach and dropper in a small bag next to the water.
So the bleach doesn't expire at the back of a cupboard
Bleach and tablets expire too. In Despendo you can log them like any other product, with a date, and the app tells you when it's time to restock.
Sources and further reading
Get the free 72-hour kit checklist
Leave your email, confirm it and we will send you the printable PDF. You will also get family preparedness tips and Despendo news. No spam, and you can unsubscribe anytime.
By subscribing you accept our privacy policy.Despendo is an independent app. This guide is general information: adapt it to your family, climate and medical needs, and always follow local authorities' instructions.
