The most reliable method
CDC and EPA agree: boiling is the most reliable method for making water safe. It kills bacteria, viruses, and parasites, including Cryptosporidium, which resists chemical disinfection.
The procedure is simple. If the water is cloudy, filter it first through a clean cloth, paper towel, or coffee filter. Bring it to a full rolling boil for one minute. At elevations above 6,500 feet, boil for three minutes. Let the water cool naturally before use. Store in a clean, covered container.
Boiling does not remove chemical contaminants. If your water advisory is about chemical contamination (fuel spill, industrial runoff) rather than microbial contamination, boiling will not help. Use bottled water or an alternate source instead.
When you cannot boil
If boiling is not possible (no fuel, no pot, no heat source), household bleach can disinfect water against most bacteria and viruses. EPA and CDC provide the dosage: for standard unscented household bleach at 6% sodium hypochlorite, add 8 drops per gallon of clear water. For the newer 8.25% concentrated bleach, use 6 drops per gallon. Double the amount if the water is cloudy.
Stir the bleach into the water and let it stand for at least 30 minutes. After 30 minutes, the water should have a faint chlorine odor. If it does not, repeat the dose and wait an additional 15 minutes. The faint smell confirms the bleach has done its job and free chlorine remains.
Only use regular, unscented liquid bleach with sodium hypochlorite as the sole active ingredient (typically 5% to 9%). Never use scented bleach, splash-less bleach, color-safe bleach, or bleach with added cleaners. Check the label before using.
Like boiling, bleach disinfection does not remove chemical contaminants. It also does not reliably kill Cryptosporidium. If you know Cryptosporidium is a concern, boiling or filtration through a certified filter is the better choice.
What to store water in, and what to avoid
CDC warns never to use containers that previously held toxic chemicals, including bleach, pesticides, petroleum products, or industrial solvents. Trace chemical residues can leach into stored water and are not removed by rinsing, even thorough triple-rinsing.
Safe options: commercially sealed bottled water (the gold standard), food-grade water storage containers from camping or preparedness suppliers, and thoroughly cleaned food-grade containers that held only food or beverages previously. Glass, food-grade plastic (look for HDPE, marked with recycling number 2), and stainless steel all work.
Milk jugs are a common but imperfect choice. The thin plastic degrades over time and milk proteins are difficult to fully remove, creating bacterial growth risk. If you use them, clean thoroughly with soapy water and a bleach rinse, fill with treated water, label with the date, and rotate every six months.
The baseline: one gallon per person per day, with additional for pets, infants, pregnant women, people who are sick, and hot climates. A family of four needs a minimum of 12 gallons for a 72-hour supply.
- Boiling: full rolling boil for 1 minute (3 minutes above 6,500 ft). Filter cloudy water first.
- Bleach (6%): 8 drops per gallon of clear water. Wait 30 minutes. Look for faint chlorine smell.
- Bleach (8.25%): 6 drops per gallon. Double for cloudy water.
- Never use: scented bleach, splash-less bleach, or containers that held chemicals.
- Storage: food-grade containers only. Label and rotate every 6 months.
- Chemical contamination: neither boiling nor bleach helps. Use bottled water.
- How to Make Water Safe in an Emergency — CDC. Boil times, bleach dosage tables, filtration guidance.
- Emergency Disinfection of Drinking Water — EPA. Bleach concentrations, alternative disinfectants, granular calcium hypochlorite.
- Safe Water Storage — CDC. Container selection, materials to avoid.
- Water — Ready.gov / FEMA. Storage amounts, household planning baseline.