1 micron or smaller
Absolute pore size of 1 micron, or certified to NSF standard 53 or 58 for cysts: removes parasites. Bacteria and viruses get through.
Water
How to purify water at home
Bring clear water to a rolling boil for 1 minute (3 minutes above 5,000 feet). If you can't boil, add 8 drops of plain 6% bleach per gallon, stir and wait 30 minutes before drinking.
Which method, when
Pick by what you have and what is in the water.
| Method | Kills germs | Removes chemicals | Use it when |
|---|---|---|---|
| Boiling | Viruses, bacteria and parasites | No | You have heat and fuel. The CDC calls it the best way to kill germs. |
| Unscented bleach | Bacteria and viruses. Works poorly on parasites | No | You can't boil, and the water is clear or has been filtered. |
| Filter | Depends on the pore size | Varies by filter | Paired with bleach or boiling, unless it's reverse osmosis. |
| Tablets or iodine | Per the product label | No | You have no bleach. Follow the label, as strengths differ. |
From the CDC and EPA pages listed under Sources.
Boiling
Boiling is the method to reach for first.
01Boil it
- If the water is cloudy, filter it first (see below).
- Bring it to a rolling boil for at least 1 minute.
- Above 5,000 feet (1,000 metres), boil for 3 minutes.
- Let it cool, then store it in clean containers with covers.
Bleach: which bottle counts
Use regular, unscented chlorine bleach that the label says is suitable for disinfection and sanitization. Scented bleach, colour-safe bleach and bleach with added cleaners won't do.
Check the label for the strength. Household bleach is usually 6% or 8.25% sodium hypochlorite, and the dose depends on which one you have.
Bleach drops per litre and gallon
The EPA's amounts for clear water.
| Water | 6% bleach | 8.25% bleach |
|---|---|---|
| 1 quart or 1 litre | 2 drops | 2 drops |
| 1 gallon | 8 drops | 6 drops |
| 2 gallons | 16 drops (1/4 tsp) | 12 drops (1/8 tsp) |
| 4 gallons | 1/3 tsp | 1/4 tsp |
| 8 gallons | 2/3 tsp | 1/2 tsp |
Double the amount if the water is cloudy, coloured or very cold. Source: EPA.
After you add it
- Stir, and let it stand for 30 minutes.
- Smell it. It should have a slight chlorine odour.
- No smell? Repeat the dose and wait another 15 minutes.
- If the taste is too strong, pour it back and forth between clean containers and let it sit for a few hours.
What filters actually remove
The CDC sorts filters by pore size. Portable filters don't remove every type of germ.
0.3 micron or smaller
Removes bacteria and parasites. Viruses get through, so add bleach or boil afterwards.
Reverse osmosis
Removes parasites, bacteria and viruses, and salt as well.
Cloudy water
Clear it before you treat it.
Filter it through a clean cloth, paper towel or coffee filter into a clean container.
Then boil it, or use bleach at double the amount in the table. The CDC also says to filter before you disinfect when you use a filter.
Where to find water worth treating
Before you go outside, check what the house already holds.
- The tank of your tap water heater (the one feeding your faucets, never the separate tank that heats radiators in some older homes).
- Ice cubes made with clean water, melted.
- The toilet tank, never the bowl, if the water is clear and has no coloured cleaner in it.
- Outside, river, lake or rain water, always treated. The EPA says flowing water is generally better than still water.
What doesn't make water safe
Some water can't be fixed at home.
- Boiling and bleach don't remove heavy metals, salts or most other chemicals.
- Water contaminated with fuel or toxic chemicals can't be made safe. Find another source.
- Avoid water with floating material, a dark colour or a questionable smell.
- Pool and spa water is for washing, not drinking.
- A portable filter on its own leaves viruses, and often bacteria, behind.
No bleach in the house?
The EPA gives iodine as a backup: 5 drops of 2% tincture of iodine per quart or litre, 10 drops if the water is cloudy or coloured, then wait at least 30 minutes.
Disinfection tablets contain chlorine, iodine, chlorine dioxide or similar agents. Follow the label on the pack, because each one has a different strength.
Questions people ask
How long do you boil water to make it safe?
A rolling boil for at least 1 minute. At altitudes above 5,000 feet, boil it for 3 minutes.
How many drops of bleach per gallon of water?
8 drops of 6% bleach, or 6 drops of 8.25% bleach, per gallon of clear water. Double it for cloudy, coloured or very cold water.
How much bleach per litre of water?
2 drops per litre for either 6% or 8.25% bleach, then wait 30 minutes.
Can I use scented bleach to purify water?
No. The EPA says to use only regular, unscented chlorine bleach, with no colour-safe formula or added cleaners.
Does a water filter make water safe to drink?
Of the filter types the CDC lists, only reverse osmosis removes viruses. With any other filter, disinfect the water after filtering.
Does boiling remove chemicals?
No. Boiling kills germs but doesn't remove heavy metals, salts or most chemicals.
