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Water

Purify water with unscented household bleach

You can use regular, unscented 5–6% sodium hypochlorite household bleach to disinfect water in an emergency when you have no suitable filter or way to boil it. A measured dose of chlorine needs enough contact time to kill many disease-causing organisms; it does not remove chemical pollutants. Never use scented, color-safe, splashless, or other additive bleach. Bleach does not reliably kill Cryptosporidium—boil or use a filter rated to remove that parasite when parasites are a concern.

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Water 30 min practice Beginner Use this method in backcountry or emergency settings where you can collect fresh water and measure its volume. Choose the clearest available source, away from sewage, industrial discharge, agricultural runoff, and algal blooms; bleach cannot make saltwater or chemically contaminated water safe.
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Topic summary

You can use regular, unscented 5–6% sodium hypochlorite household bleach to disinfect water in an emergency when you have no suitable filter or way to boil it. A measured dose of chlorine needs enough contact time to kill many disease-causing organisms; it does not remove chemical pollutants. Never use scented, color-safe, splashless, or other additive bleach. Bleach does not reliably kill Cryptosporidium—boil or use a filter rated to remove that parasite when parasites are a concern.

Key takeaways

  • Your water is reasonably clear before you add bleach.
  • You have checked the bleach concentration and measured both the water volume and the appropriate drop count.
  • The full contact time has elapsed, including any additional wait after a repeat dose.
  • The water has a slight chlorine smell before aeration and remains protected in a clean, covered container.
  • Avoid: Using bleach of an unknown concentration makes the drop count unreliable; check that the label specifies 5–6% sodium hypochlorite before following this procedure.
  • Avoid: Using old or heat-damaged bleach can leave too little active chlorine; use a fresh, properly stored supply.

Intended uses

  • Water skill (Beginner, ~30 min practice)
  • Requires: Clean dropper, Clean, marked container for measuring and treating water, Second clean container for settling or aerating, Clean cloth, Watch or timer

Climate suitability

Use this method in backcountry or emergency settings where you can collect fresh water and measure its volume. Choose the clearest available source, away from sewage, industrial discharge, agricultural runoff, and algal blooms; bleach cannot make saltwater or chemically contaminated water safe.

Safety: Keep concentrated bleach out of your eyes and off your skin, and never mix it with acids, ammonia, or other cleaners. A chlorine smell is only a practical treatment check, not proof that the water is free of every hazard.

Required tools

  • Clean dropper
  • Clean, marked container for measuring and treating water
  • Second clean container for settling or aerating
  • Clean cloth
  • Watch or timer

Required materials

  • Regular, unscented household bleach labeled 5–6% sodium hypochlorite, with no added cleaners or fragrances
  • Collected fresh water

Step-by-step

  1. Filter cloudy water through cloth or let it settle until reasonably clear.

    Why: 1. Filter cloudy water through cloth or let it settle until reasonably clear. Suspended particles can shield organisms and consume chlorine, making disinfection less dependable; if you settle the water, gently pour off the clearer portion without disturbing the sediment.

  2. Add 2 drops of unscented 5–6% household bleach per liter of clear water; use 4 drops per liter if the water is cold or still turbid.

    Why: 2. Add 2 drops of unscented 5–6% household bleach per liter of clear water; use 4 drops per liter if the water is cold or still turbid. Measuring both the water and the bleach keeps the treatment dose appropriate, while the higher dose helps compensate for slower action in cold water or chlorine consumed by remaining material.

  3. Stir and let stand for at least 30 minutes.

    Why: 3. Stir and let stand for at least 30 minutes. Mixing distributes the chlorine throughout the water, and the waiting period gives it time to act; start timing after you finish mixing.

  4. The water should have a slight chlorine smell. If not, repeat the dose and wait another 15 minutes.

    Why: 4. The water should have a slight chlorine smell. If not, repeat the dose and wait another 15 minutes. A faint remaining odor suggests that some chlorine remains after reacting with material in the water, while repeating the measured dose addresses an initial dose that may have been exhausted.

  5. If chlorine taste is too strong, pour between two clean containers a few times to aerate before drinking.

    Why: 5. If chlorine taste is too strong, pour between two clean containers a few times to aerate before drinking. Aeration can reduce the chlorine taste, but you should do it only after the full treatment time so you do not reduce chlorine before it has finished acting.

Common mistakes

  • Using bleach of an unknown concentration makes the drop count unreliable; check that the label specifies 5–6% sodium hypochlorite before following this procedure.
  • Using old or heat-damaged bleach can leave too little active chlorine; use a fresh, properly stored supply.
  • Guessing the water volume or pouring bleach directly from its bottle gives an uncertain dose; use a marked container and a dropper.
  • Treating muddy water without clearing it first can undermine disinfection; settle or strain it before dosing.
  • Returning treated water to a dirty container can recontaminate it; keep it covered in a clean container and avoid touching its inside or rim.

Troubleshooting

  • If water remains visibly cloudy, then settle it longer or strain it again, and use the higher dose if some turbidity remains.
  • If the water is very cold, then use the higher dose and extend the initial contact time to at least 60 minutes.
  • If there is still no slight chlorine smell after the repeat dose and additional wait, then do not keep adding bleach indefinitely; obtain fresh bleach, change sources, or use another suitable treatment method.
  • If you accidentally add much more bleach than intended, then discard the batch and start again rather than relying on aeration to correct the dose.

Field practice drill

Practice with one liter of clear tap water, a marked container, a dropper, and the correct bleach. Read the label, add two drops, stir, and set a 30-minute timer; while you wait, rehearse clearing cloudy water with a separate batch and identify how you would protect treated water from contamination. At the end, check for a slight chlorine smell and rehearse the repeat-dose decision; allow extra time if another dose is needed, and do not drink the practice water merely to demonstrate the skill.

Indicators of success

  • Your water is reasonably clear before you add bleach.
  • You have checked the bleach concentration and measured both the water volume and the appropriate drop count.
  • The full contact time has elapsed, including any additional wait after a repeat dose.
  • The water has a slight chlorine smell before aeration and remains protected in a clean, covered container.

Related outdoor skills

Educational reference only. Wilderness conditions change fast — practice in low-stakes settings, take a certified wilderness first-aid course, and confirm regional regulations before you rely on any of these skills in the field.