In an emergency, filtering water through a cloth removes debris, but you must then boil or disinfect with bleach to kill harmful microbes before drinking.
When a natural disaster or utility failure cuts off safe tap water, finding a drinkable source becomes urgent. Filtration alone — even through a clean cloth or coffee filter — removes dirt but does not disinfect. Below are the steps that the EPA, CDC, and American Red Cross recommend for making emergency drinking water in a U.S. home.
Start by Removing Particles
Cloudy or muddy water must be pre-filtered first, because sediment can shield microbes from heat or bleach. Pour the water through a clean cloth, paper towel, or coffee filter. If no filter cloth is available, let the water sit until sediment settles to the bottom, then carefully pour off the clearer top layer into a clean container. This step does not make the water safe — it only prepares it for disinfection.
Boiling: The Most Reliable Method
Bring the pre-filtered water to a full rolling boil and let it continue boiling for at least 1 minute. At elevations above 6,500 feet, extend the boil time to 3 minutes because water boils at a lower temperature, which is less effective at killing pathogens. After boiling, let the water cool naturally, then pour it into clean, sanitized containers with tight lids. Boiling cannot remove chemical contamination from fuel or heavy metals, but for microbiological safety it is the gold standard.
Chemical Disinfection with Unscented Bleach
If you cannot boil water, unscented household bleach that contains 5.25% to 6% sodium hypochlorite is the next best option. Use only regular, unscented bleach — never splashless, scented, or gel formulations.
For clear pre-filtered water, add 8 drops of bleach per 1 gallon (the CDC guideline) or 16 drops per gallon (the Red Cross guideline — using the same bleach concentration). Stir or shake the container well, then wait 30 minutes. The water should have a faint chlorine smell. If no chlorine smell remains after 30 minutes, add the same dose again and wait another 30 minutes. If there is still no smell, discard the water and find a different source. Bleach works best in cool water; never add it to hot water.
| Disinfection Method | Dosage / Time | When to Use |
|---|---|---|
| Boiling (sea level) | Rolling boil for 1 minute | First choice; any clear or pre-filtered water |
| Boiling (above 6,500 ft) | Rolling boil for 3 minutes | Mountain or high-elevation emergencies |
| Unscented bleach | 8-16 drops per gallon; wait 30 min | When boiling is not possible |
Three Mistakes That Can Leave Water Unsafe
The most common error is assuming clear water is safe to drink — visual clarity is not the same as microbiological safety. Another frequent mistake is shortening the boil time or only bringing water to a simmer rather than a full rolling boil. Finally, using the wrong bleach is dangerous: scented, splashless, or concentrated laundry bleach may contain additives or levels of chlorine that are not suitable for emergency disinfection. Stick to unscented household bleach with 5.25% to 6% sodium hypochlorite, and store it away from heat and light to preserve its strength.
FAQs
Can a DIY sand and charcoal filter make water safe?
Always follow a sand filter with boiling or chemical disinfection before drinking.
Does boiling water remove chemical contamination?
Boiling kills microbes but does not remove chemicals, fuels, pesticides, or heavy metals. If you suspect chemical contamination, seek a different water source or use an activated-carbon filter in addition to disinfection.
What if I cannot detect a chlorine smell after adding bleach?
If after 30 minutes there is no faint chlorine odor, double the dose and wait another 30 minutes. If the smell still does not appear, the water may contain high levels of organic material or ammonia — find a different source.
References & Sources
- EPA. “Emergency Disinfection of Drinking Water.” Recommends rolling boil for at least one minute.
- CDC. “Make Water Safe During an Emergency.” Specifies 1-minute boil, 3-minute boil above 6,500 ft, and 8 drops of bleach per gallon.
- American Red Cross. “Water Treatment | Safe Drinking Water.” Provides pre-filter, boil, and bleach dosage guidance for emergency water safety.