Water · Updated
How to make water safe to drink: boiling, bleach, filters and tablets
How do I make water safe to drink in an emergency?
Boil clear water at a rolling boil for one minute, or three minutes at high elevation. If you cannot boil, add plain unscented bleach using the EPA drop table and wait 30 minutes. Filters alone do not remove viruses; purification tablets do. Let cloudy water settle and strain it first.
The short answer
Boil it if you can. If you cannot, use plain bleach or purification tablets. A filter helps with dirt and germs like bacteria and parasites, but most small filters do not stop viruses. When in doubt, filter first, then boil or treat.
Store clean water first so you rarely need this: see how much water to store.
Step 1: Clear cloudy water first
Cloudy water makes boiling and bleach less reliable. The EPA says cloudy water should be settled and filtered first. Let it stand until the dirt sinks, then pour the top through a clean cloth, paper towel or coffee filter into a clean container.
Option 1: Boil it
The CDC says to bring clear water to a rolling boil for 1 minute, and for 3 minutes at elevations above 6,500 feet. The EPA uses 5,000 feet as its cutoff. If you live near either number, choose 3 minutes.
- Heat until big bubbles roll across the whole surface.
- Start timing once it is rolling.
- Turn off the heat and let it cool naturally.
- Pour into a clean, covered container.
Boiled water can taste flat. The EPA says you can add one pinch of salt per quart or pour it between two clean containers a few times.
If the power is out, use a safe method to heat water. See cooking without power safely.
Option 2: Plain bleach
Use household bleach that is plain and unscented, with no added cleaners. Check the label for its strength: 6% or 8.25% sodium hypochlorite. The EPA table gives:
| Water | 6% bleach | 8.25% bleach |
|---|---|---|
| 1 quart or liter | 2 drops | 2 drops |
| 1 gallon | 8 drops | 6 drops |
| 2 gallons | 16 drops (1/4 teaspoon) | 12 drops (1/8 teaspoon) |
| 4 gallons | 1/3 teaspoon | 1/4 teaspoon |
| 8 gallons | 2/3 teaspoon | 1/2 teaspoon |
Then:
- Stir the water.
- Wait 30 minutes. It should smell faintly of chlorine.
- If it does not, repeat the dose and wait another 15 minutes.
- For cloudy, colored or very cold water, double the bleach.
If the taste is too strong, pour it between clean containers and let it stand for a few hours.
Option 3: Purification tablets
Tablets are small, light and long-lasting. Follow the package directions exactly, especially the wait time, which can be 30 minutes or up to four hours for some products. Chlorine dioxide tablets are rated by CDC as highly effective against viruses when used correctly (an older CDC guide, now archived).
Water
Water purification tablets
Aquatabs · 397 mg, 100 pack
Backup way to make water safe when you cannot boil it.
Filters versus purifiers
A filter strains out dirt, bacteria and parasites. An older CDC guide in its archive explains that filters with pores of 0.1 to 0.3 microns remove bacteria and protozoa but not viruses, and says to disinfect after filtering. A purifier also deals with viruses, using chemicals, a special filter or both.
So the safe approach for water from a river, lake or unknown tap is:
- Strain out the visible dirt.
- Filter it.
- Then boil or treat it with tablets or bleach.
Water from a clean city supply that is only under a short boil advisory is usually fine with a boil alone.
Sawyer Squeeze
A squeeze filter screws onto a pouch or bottle. Fill the pouch, screw on the filter, squeeze water through into a clean container or mouth. After use, flush clean water backward through it, as the maker explains. Follow the maker's storage directions, and do not let it freeze. Treat the filtered water for viruses if the source could carry them.
Water
Squeeze water filter
Sawyer · Squeeze SP129
Filters water from a puddle, tank or tap so your family can drink safely.
Gravity filter
A gravity filter has an upper tank and a lower tank. Fill the top with water, wait for it to drip through, and drink from the bottom. It makes enough for a family with no pumping. Check whether your model is tested for viruses; if not, treat the water after.
Water
Family gravity water purifier
LifeStraw · Family 2.0, 12 L
If tap water is unsafe, this cleans water for the whole family by gravity alone, with no power and no pump.
After you treat it
- Store water in clean, covered containers.
- Write the date and "treated" on them.
- Use the water within a few days if you treated it in an open container.
- Keep a small first-aid note about stomach illness: vomiting or diarrhea with fever means you should seek help.
Next steps
- Store water before you need to: how much water to store.
- Plan the first days: the 72-hour blackout plan.
- Handle waste if the water stops: emergency toilet with no water.
- See the Blackout Kit.
Questions
Does a water filter make water safe?
Not always. Common camping filters remove bacteria and parasites but not viruses. After filtering, treat the water with boiling or purification tablets if viruses could be present.
How long do I boil water?
CDC says bring clear water to a rolling boil for 1 minute, and for 3 minutes above 6,500 feet. The EPA gives a lower elevation of 5,000 feet for the 3-minute rule, so if you live above 5,000 feet, boiling for 3 minutes is the safe choice.
Can I use any bleach?
Use plain household bleach with no scent, no color-safe additives and no cleaning boosters. Check the label for the strength, then use the matching row of the EPA table.
Does boiling remove chemicals?
No. Boiling and bleach do not remove heavy metals, salts or most chemicals. If officials say the water is chemically contaminated, use bottled water.
Sources
This guide is general information, not medical, legal or electrical advice. In an emergency, call 911 or your local emergency number.