How to Disinfect Emergency Drinking Water

Start by identifying the hazard

Use bottled water if available. A boil-water advisory usually concerns germs and includes local instructions. A do-not-drink or do-not-use advisory may involve chemicals or other hazards; boiling or chlorination can fail to make water safe. Never treat water with fuel, toxic chemicals, saltwater, or an unknown spill using a generic recipe.

Boiling

If water is cloudy, let it settle and filter it through a clean cloth, paper towel, or coffee filter. Bring the clearer water to a rolling boil for at least 1 minute. CDC’s current page calls for 3 minutes above 6,500 feet; EPA’s emergency page says 3 minutes above 5,000 feet. The federal pages therefore differ. PHS practical recommendation: when local authorities have not given an instruction, use EPA’s lower altitude threshold as the more conservative household choice. Cool naturally and store in a clean, covered container.

Plan the whole boiling capability

Water + heat source + fuel/energy + appropriate vessel + safe operating location + safe handling + cooling + clean post-treatment storage. Fuel is part of water preparedness: a camp stove with no fuel is not a complete boiling capability.

Match the heat source to the emergency

• Normal utilities available: during a local boil-water advisory, a functioning household stove may be appropriate if it is safe to operate.
• Utility outage: plan an appropriate propane/camp stove or other outdoor cooking appliance, with its required fuel. Use it only in the location and manner specified by its manufacturer.
• Prolonged or austere conditions: a suitable, properly installed and vented wood stove may be an option only if its instructions permit cooking. An outdoor fire needs an appropriate heat-safe vessel, stable cooking support, safe handling tools and sufficient fuel. Follow local fire restrictions and conditions.

Prevent burns, fire and carbon-monoxide poisoning

• Choose a heat-safe cooking vessel compatible with the appliance and large enough for the planned batch; ensure the support can hold it securely. Plan manageable batches rather than a dangerously heavy pot.
• Have adequate fuel/energy and follow the appliance’s operating and fuel-handling instructions. Never use outdoor-only combustion appliances indoors or in enclosed spaces, including tents and garages. Portable gas camp stoves and charcoal must not be used indoors.
• Use dry heat-resistant gloves, oven mitts or potholders and appropriate long-handled tools. Keep the setup stable and attended; protect against tipping, spills and scalding.
• Keep children and pets away from heat sources, hot vessels and hot water.
• After the required rolling-boil time, let water cool naturally to a safe temperature before drinking, transferring or handling it. Use a clean, sanitized, appropriate container with a tight cover; avoid recontamination.

See CDC carbon-monoxide precautions, U.S. Fire Administration burn prevention, CPSC equipment stability and instructions and National Park Service campfire safety. These practical preparations do not change the boiling times above or make chemical contamination safe.

Unscented household bleach: keep the protocols separate

Use fresh, regular, unscented liquid household chlorine bleach suitable for disinfection, with a known sodium-hypochlorite concentration and no added cleaners. Follow label directions for drinking-water disinfection when supplied. Do not use scented, color-safe or splashless products. First settle and prefilter cloudy water; this is only preparation, not disinfection.

Both sources say to double their listed dose for cloudy, colored or very cold water (CDC also says murky). They publish different concentration tables; do not average the doses or silently combine them. CDC’s drop and milliliter measurements are the alternatives it publishes, not a calibrated conversion for every dropper. Use an appropriate measuring device, never a capful.

PHS practical recommendation: Keep a copy of the complete instructions that match your product. If following EPA’s process and there is still no slight chlorine odor after repeating the dose, use another safe supply and seek health-department advice. Odor is not a test for chemical safety. Bleach is less reliable than boiling against some parasites. Never mix bleach with ammonia, acids, or other cleaners.

What these methods cannot do

Boiling and bleach disinfect against many germs; they do not remove most chemical contaminants, metals, salts, or toxins. Boiling can concentrate some chemical contaminants as water evaporates. Some parasites resist chemical disinfectants; boiling is generally the more reliable emergency method for microbes when feasible. Follow CDC/EPA information and local instructions.

Official source and related reading

Detailed procedures and tables: CDC — How to Make Water Safe in an Emergency and EPA — Emergency Disinfection of Drinking Water.

Related: filter vs. purifier vs. disinfection, well-water planning, and calcium hypochlorite cautions.

Common mistakes

• Using scented, splashless, color-safe, or cleaner-added bleach.
• Guessing the concentration or mixing a treatment dose by “capful.”
• Disinfecting cloudy water without settling and prefiltering.
• Assuming any chlorine smell proves water is safe.
• Boiling water under a chemical do-not-use advisory.

Related Guides

• Should You Store Reverse-Osmosis Water for Emergencies?
• Water Filter vs. Purifier vs. Disinfection: What’s the Difference?
• Can Calcium Hypochlorite (Pool Shock) Treat Emergency Drinking Water?
• Choosing Emergency Water Containers: Size, Weight, and Practical Storage

Return to the Emergency Water Preparedness Guide