Making Water Safe: Boiling, Bleach, and Purification Tablets

Not medical advice. This guide covers treating water, using public-health guidance. Follow your local health department's instructions during a boil-water notice, and ask a doctor about any health concerns.

What it's for

When the tap is off or under a boil notice, or all you've got is a creek, you need a way to make water safe. Ready.gov says to treat any water of uncertain quality before you drink it, wash food or dishes with it, brush your teeth with it, or make ice. That goes for the stock tank and the irrigation ditch too.

Ready.gov calls boiling the safest method, and the CDC calls it the best way to kill germs. Bleach and tablets are lighter and need no fuel. Knowing all three gives the Cookie options.

Before you need it (practice)

• Know your elevation. The CDC says boil for 1 minute, or 3 minutes above 6,500 feet. Look up your home and cabin elevations and write them on the kit card.
• Check your bleach label. Use plain, unscented household bleach: no scented, color-safe, or added-cleaner kinds (Ready.gov). Note the sodium hypochlorite percentage on the label.
• Pack a dropper with the bleach. Drops are easier to get right than spoon guesses.
• Read your tablet package now. Wait times and water amounts vary by product.

Step by step

First, for any method: if the water is cloudy, let it settle and draw off the clear water, or strain it through a clean cloth, paper towel, or coffee filter (CDC).

Boiling (best)

1. Bring clear water to a rolling boil for 1 minute (3 minutes above 6,500 ft) (CDC).
2. Let it cool.
3. Store it in clean, sanitized containers with tight covers.
4. Flat taste? Pour it back and forth between two clean containers (CDC, Ready.gov).

Unscented bleach

1. Follow the bleach label's drinking-water directions if it has them (CDC).
2. If not, for bleach labeled 5% to 9% sodium hypochlorite, the CDC table says: 8 drops per gallon (about ½ mL), 2 drops per quart or liter, 40 drops per 5 gallons. For cloudy, colored, or very cold water, double it. (The CDC has a separate table for 1% bleach.)
3. Stir well and wait at least 30 minutes (CDC).
4. Ready.gov adds: the water should have a slight bleach smell. If it doesn't, repeat the dose and wait another 15 minutes. If there's still no chlorine smell, throw it out and find another source.

Purification tablets or drops

1. Follow the label exactly. Each product treats a set amount of water and has its own wait time (CDC).
2. Know what you're using. The CDC notes iodine and chlorine tablets kill most germs but not Cryptosporidium. Chlorine dioxide tablets will, when used correctly, usually with a longer wait.
3. The CDC says people who are pregnant, have thyroid problems, or are sensitive to iodine should avoid iodine-treated water, and no one should drink it for more than a few weeks at a time.

Common mistakes

• Using scented or "splash-less" bleach. Plain, unscented only.
• Skipping the wait. The clock starts after you stir.
• Boiling a pot of mud. Settle or strain it first.
• Expecting any of this to fix chemical or fuel contamination. The CDC says boiling and disinfecting won't make water with fuel, toxic chemicals, or radioactive material safe. Use bottled water or another source and ask your health department.
• Using heating-system water. The CDC says never drink water from radiators or boilers.

Care & storage

• Mind the bottle's date. Check for a date code or "best by" on your bleach and replace the kit bottle when it's past it. Ask the manufacturer if you can't find one.
• Tablets have expiration dates. Keep them sealed, dry, and in the kit.
• Store treated water in clean, sanitized, covered containers (see Storing and Rotating Water).

Related gear

• Water purification tablets · Unscented household bleach
• Backpacking stove · Fuel canister · Cook pot
• Pair with: How to Use a Squeeze Water Filter
• Category: Water · Role: Cookie

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