The tap is the one utility everybody assumes. Then the boil notice comes, or the pressure drops to a trickle after a main breaks, or the well pump goes quiet because the power did, or floodwater backs into the system. Whatever the cause, what comes out of the faucet, if anything does, is no longer something you should drink straight.
I have been on enough post-storm calls to know how this plays out. The stomach bugs show up two or three days in, and they hit the people who figured the water looked fine.
Here is how I make questionable water safe, in the order I trust each method. One rule covers all of them: nothing below fixes water with fuel, pesticides, or industrial chemicals in it. If it smells like gasoline or has a sheen on top, find different water.
Boiling: the one I trust most
Boiling kills everything living in water: bacteria, viruses, and the protozoa like Giardia and Cryptosporidium that shrug off chemicals. It needs no special gear and does not care how cheap your pot is.
Bring it to a full rolling boil and hold it there for one minute, or three minutes above roughly 6,500 feet. Let it cool and store it in a clean container with a tight lid. If it tastes flat, pour it back and forth between two clean containers to put air back in it.
The catch is fuel and time. A rolling boil eats propane, one pot at a time, while everybody waits. Everything below exists because you cannot always boil.
Bleach: cheap, fast, and already in your house
Plain unscented household bleach is the best emergency water treatment nobody buys on purpose. It kills bacteria and viruses. It does not reliably kill Cryptosporidium and needs a long contact time for Giardia, which is why it is the backup, not the standard.
Check the label for the strength. Most bleach on the shelf today is 6% or 8.25% sodium hypochlorite.
- 6% bleach: 8 drops per gallon, about 1/8 teaspoon.
- 8.25% bleach: 6 drops per gallon.
- Either strength: 2 drops per quart.
- Cloudy, colored, or very cold water: double the dose.
Stir it in and wait 30 minutes before you drink. The water should have a faint chlorine smell. If it does not, dose it again and wait another 15 minutes.
Regular unscented bleach only: no splashless, no scented, nothing with added cleaners. Bleach also weakens as it sits, so buy a fresh bottle each hurricane season, date it, and tape a medicine dropper to the side.
Iodine and purification tablets
Tablets are the go-bag version of bleach. Chlorine and iodine tablets kill bacteria and viruses, with the same weakness against protozoa. Chlorine dioxide tablets are the exception: given the full contact time on the label, which runs to hours, they can handle Cryptosporidium too. Read the label before the emergency; every brand has its own dose and wait time.
Iodine comes with rules. Skip it if you are pregnant, have a thyroid condition, or are allergic to iodine, and nobody should drink iodine-treated water for more than a few weeks. With 2% tincture, it is 5 drops per quart of clear water, 10 if cloudy, then a 30-minute wait.
Filters: what they catch and what they miss
This is where the marketing gets ahead of the science.
A hollow-fiber filter, the kind inside most personal purifiers and straws, is rated around 0.1 to 0.2 micron. That is small enough to catch bacteria and protozoa, the bugs behind most waterborne illness. It is not small enough to catch viruses, which pass right through. If the water could have sewage in it, and after a flood that describes most of it, filter it and then boil it or bleach it. The CDC's guidance is the same: filter first, then disinfect.
Filters also do not remove dissolved chemicals, salt, or fuel. A carbon stage improves taste; it is not a fix for a contaminated source.
Here is what I stock and why. One hollow-fiber personal purifier per person: it draws from a bucket, a creek, or a storage bladder, and it is manufacturer-rated rather than independently certified, which I say on the product page. For more volume, the 0.01 micron ultrafiltration unit is rated for 4,000 liters and fills a bottle in about a minute. Same honest limits: manufacturer-rated, bacteria and protozoa, not viruses. And a straw filter in the glove box for the day you are separated from everything else. A straw is a backup layer, not a plan.
UV light: works, with conditions
Battery-powered UV pens kill bacteria, viruses, and protozoa in small batches of clear water, a liter or two at a time. The catch is the word clear: particles in cloudy water shade germs from the light, so pre-filter first, every time. And it is only as good as your battery supply.
Sunlight is the no-battery version. Fill clear plastic bottles with clear water and lay them on their side in full sun for six hours, or two full days if it is cloudy. Slow, a last resort, and free.
Distillation: the only one that handles salt and chemicals
Everything above kills germs and does nothing else. Distillation also leaves behind salt, heavy metals, and most chemicals, because you collect the steam and abandon whatever was dissolved.
The stovetop version: fill a pot halfway, tie a cup to the lid handle so it hangs upright when the lid is flipped over and does not touch the water, and boil for 20 minutes. Steam condenses on the lid and drips into the cup. That is your drinking water.
It is slow and burns fuel, so it is not how you make ten gallons a day. It is for the water nothing else can fix.
Cloudy water: clean it up before you treat it
Every method above works better on clear water, and two of them, bleach and UV, barely work without it.
Run it through a clean cloth, a paper towel, or a coffee filter to pull out the visible junk. Or let it sit until the sediment drops, then pour the clear water off the top without stirring up the bottom. A collapsible 10-liter carrier is what I use for hauling and settling; it stands on its own and folds flat when empty. Then treat the clear water like any other.
Pre-filtering removes dirt, not germs. It is step one, not the whole job.
Which method for which threat
| Method | Bacteria | Protozoa (Giardia, Crypto) | Viruses | Chemicals, salt, fuel | Notes |
|---|---|---|---|---|---|
| Boiling | Yes | Yes | Yes | No | The standard. |
| Bleach | Yes | Giardia with time, Crypto no | Yes | No | 30 minutes. Double for cloudy water. |
| Iodine | Yes | Giardia with time, Crypto no | Yes | No | Not for pregnancy or thyroid conditions. |
| Chlorine dioxide tablets | Yes | Yes, with hours of contact | Yes | No | Follow the label. |
| Hollow-fiber filter | Yes | Yes | No | No | Then boil or bleach if sewage is possible. |
| UV light | Yes | Yes | Yes | No | Clear water only. |
| Sunlight (SODIS) | Reduces all three, slowly | No | Last resort. Clear water, full sun. | ||
| Distillation | Yes | Yes | Yes | Most | Slow. The only fix for salt. |
What I'd buy first
If the budget is tight, here is the order I would spend in.
- A fresh bottle of unscented bleach and a dropper. A few dollars at any grocery store, treats hundreds of gallons, and I do not sell it. Buy it today anyway.
- One hollow-fiber purifier per person, or the press-filter bottle if you are away from the house most of the day. Same limits either way. This is what makes stored bladder water drinkable.
- A 30-gallon storage bladder, filled from the tap while the water is still clean. The cheapest treatment is the water you never had to treat.
- A collapsible carrier for every vehicle. Hauling from a distribution point is a real job, and milk jugs from the recycling bin do not survive it.
- The 105-gallon reserve bladder, once the basics are covered and if you have the floor space. Filled from the tap before the notice, that is close to a month of drinking water for a family of four.
None of this is complicated, but all of it is slower than a tap, which is the real argument for storing water before the notice comes. If you have not worked out how much to keep on hand, start with how much water to actually store for an emergency. Treating water is for when that runs out.
Know your bleach strength, keep the pot handy, and filter before you drink.
Stand Ready. Stay Unbreakable.