You can make purified water at home using several proven methods, from simply boiling it on the stove to building a basic distillation setup. The CDC ranks boiling as the single best way to kill germs in water, and it works in minutes. But depending on what you’re trying to remove, whether that’s bacteria, chemicals, or heavy metals, some methods work better than others. Here’s how each one works and when to use it.
Boiling: The Simplest Method
Bringing water to a full rolling boil for one minute kills virtually all disease-causing organisms, including bacteria, viruses, and parasites. If you live above 6,500 feet in elevation, extend that to three minutes because water boils at a lower temperature at altitude, and pathogens need more time to be destroyed.
Boiling is effective against biological contaminants, but it won’t remove chemicals, heavy metals, or dissolved solids. If your concern is specifically chemical contamination (from a spill, agricultural runoff, or old pipes), boiling alone isn’t enough. It also concentrates any minerals or metals already in the water, since pure water leaves as steam while everything else stays behind. For biological safety in an emergency, though, boiling is the go-to.
Let boiled water cool naturally before storing it. If the water tastes flat afterward, pouring it back and forth between two clean containers a few times adds air back in and improves the taste.
Distillation: Removing Nearly Everything
Distillation takes boiling a step further. Instead of just heating the water and letting it cool in the same pot, you capture the steam and condense it back into liquid in a separate, clean container. What you’re left with is water that’s been separated from nearly all its impurities: bacteria, parasites, heavy metals, salts, and most chemicals.
To distill water at home, you need a large pot with a lid, a heat-resistant bowl that floats or sits inside the pot, and ice. Fill the pot partway with water, place the bowl inside so it floats on the surface, then invert the lid and place ice on top. As water boils, steam rises, hits the cold lid, condenses into droplets, and drips down into the bowl. The collected water in the bowl is distilled.
Distillation has one notable gap: it cannot remove certain pesticides, volatile organic compounds, or volatile solvents. These chemicals have boiling points lower than or close to water’s, so they evaporate and recondense right along with the steam. If you suspect these contaminants are present, pair distillation with an activated carbon filter for more thorough purification.
Activated Carbon Filtration
Activated carbon filters work through adsorption, meaning contaminants physically stick to the surface of the carbon as water passes through. This makes them particularly effective at removing the chemical contaminants that boiling and distillation miss. Carbon filters reliably remove chlorine, volatile organic compounds, pesticides, benzene, trihalomethanes, and chlorinated solvents. They’re also moderately effective at reducing some heavy metals.
You’ll find activated carbon in pitcher filters, faucet-mounted filters, and under-sink systems. For home purification, running water through a carbon filter after boiling or distilling it gives you broad protection against both biological and chemical contaminants. Carbon filters do need regular replacement, since once the surface is saturated with captured chemicals, they stop working. Follow the manufacturer’s replacement schedule for your specific filter.
Chemical Disinfection With Bleach
When you can’t boil water, household bleach is an effective backup for killing bacteria, viruses, and most parasites. Use only regular, unscented liquid bleach with sodium hypochlorite as the active ingredient. Scented bleach, color-safe bleach, or bleach with added cleaners can introduce harmful chemicals.
The EPA recommends the following amounts per gallon of clear water:
- 6% bleach: 8 drops per gallon
- 8.25% bleach: 6 drops per gallon
If the water is cloudy, colored, or very cold, double those amounts. After adding bleach, stir and let the water stand for at least 30 minutes. You should detect a faint chlorine smell. If you don’t, repeat the dose and wait another 30 minutes. Like boiling, bleach disinfection handles biological threats but does nothing for chemical contaminants.
Water Purification Tablets
Iodine and chlorine dioxide tablets are portable alternatives designed for hiking, travel, and emergencies. Drop the tablet into your water container, wait for it to dissolve, then let the water sit for at least 30 minutes before drinking.
Temperature matters significantly with tablets. In cold water below 40°F (4°C), you should double the wait time. Research has shown that at 50°F, only 90% of Giardia cysts (a common waterborne parasite) are inactivated after 30 minutes. Warmer water, ideally at least 68°F, produces much more reliable results. Tablets are convenient and lightweight, but they’re best treated as an emergency or travel solution rather than a daily purification method.
UV Light Purification
Ultraviolet light disrupts the DNA of bacteria, viruses, and parasites so they can no longer reproduce or cause infection. Portable UV purifiers (pen-style devices you swirl in a water bottle) and UV-equipped home water systems both use this principle. UV treatment is chemical-free and leaves no taste or odor.
Research has demonstrated that UV light at standard doses effectively inactivates even high concentrations of both gram-negative and gram-positive bacteria. It’s also proven effective against Cryptosporidium, a parasite that resists chlorine disinfection. The key limitation is that UV light only works well in relatively clear water. Particles and sediment create shadows where microorganisms can hide from the light. If your water is cloudy, filter it through a cloth or let sediment settle out before UV treatment.
Like boiling and chemical methods, UV light handles living organisms but doesn’t remove dissolved chemicals or heavy metals.
Solar Disinfection (SODIS)
If you have no fuel, electricity, or chemicals, sunlight itself can purify water. The SODIS method involves filling clean, clear PET plastic bottles (standard soda or water bottles) with water and placing them in direct sunlight. On sunny days, 6 hours of exposure is sufficient. On cloudy days, the required time jumps to 48 hours. On days of continuous rainfall, SODIS isn’t reliable enough to use.
The water should have a turbidity below 30 NTU, which roughly means you should be able to see through it clearly. If it’s murky, filter it through a clean cloth first. SODIS bottles should be no larger than 2 liters, since UV rays can’t penetrate deeply enough in bigger containers. This method is used extensively in developing regions and is well-validated by research, but it requires patience and sunshine.
Combining Methods for Best Results
No single purification method removes everything. Boiling, UV, bleach, and tablets handle biological contaminants effectively but leave chemicals untouched. Distillation removes most contaminants but misses volatile chemicals. Carbon filtration excels at chemicals but may let certain viruses through.
The most thorough approach for home use combines two methods: a biological treatment (boiling or UV) paired with an activated carbon filter. This covers bacteria, viruses, parasites, chlorine, pesticides, and volatile organic compounds. If you’re preparing for an emergency, the practical order is to filter cloudy water through cloth first, then boil it, and finally pass it through a carbon filter if one is available.
Storing Purified Water Safely
Purified water can be recontaminated by a dirty container. The CDC recommends using FDA-approved food-grade water storage containers, which won’t leach toxic substances into your water. If you don’t have a food-grade container, choose one made of durable, unbreakable material with a tight-fitting lid and, ideally, a narrow neck or opening that limits contact with hands and airborne contaminants.
Never reuse containers that previously held bleach, pesticides, or other toxic chemicals, even if you’ve washed them thoroughly. Residues can persist in the plastic. If you’re storing purified water for emergencies, replace it every six months to keep it fresh.