How to Treat Water: Official Figures

Follow local advisories first. Bottled water is the safest choice. Treatment cannot make water safe if it contains fuel, chemicals or radioactive material. In that case, use another source and call your health department.

Boiling: best option

1. If the water is cloudy, let it settle, or filter through clean cloth, paper towel or a coffee filter.
2. Bring to a rolling boil for 1 minute.
3. At high elevation, boil longer. CDC says 3 minutes above 6,500 ft (about 2,000 m). Health Canada says at least 2 minutes above 2,000 m (about 6,500 ft). I use the longer time.
4. Let it cool, and store it in clean, covered containers.

A pinch of salt per quart or litre, or pouring between containers, improves flat taste.

Bleach

Use unscented liquid household chlorine bleach. Check the label’s strength. Stir, then wait at least 30 minutes before drinking. Use a clean dropper.

Water	Bleach 5% to 9% (CDC)	Bleach 1% (CDC)
1 quart or litre	2 drops	10 drops (⅛ tsp, ½ mL)
1 gallon (3.8 L)	8 drops	40 drops (½ tsp, 2½ mL)
5 gallons (19 L)	40 drops (½ tsp, 2½ mL)	200 drops (2½ tsp, 12½ mL)

If the water is cloudy, murky, coloured or very cold, double the amount (CDC).

In Canada, Health Canada says about 2 drops of unscented 5.25% bleach per 1 litre (4 cups), left for 30 minutes. FDA gives 8 drops (⅛ tsp) per gallon (3.8 L) for 5.25% bleach, and ¼ tsp per gallon for cloudy water. If your bleach is another strength, use the CDC table above or its label directions.

FDA notes that bleach and chlorine or iodine tablets will not kill parasitic organisms. If parasites are a concern, boil the water.

Tablets and drops

Follow the label. These kill most viruses and bacteria but may not kill parasites. Iodine and chlorine tablets do not kill Cryptosporidium, but chlorine dioxide tablets do if used correctly. Do not drink iodine-treated water if you are pregnant, have thyroid problems or are sensitive to iodine, and no one should drink it for more than a few weeks at a time.

Filters

Portable filters do not remove viruses. CDC lists a pore size of 1 micron or smaller for parasites like Giardia and Cryptosporidium, and 0.3 micron or smaller for bacteria. After filtering, add a disinfectant to deal with viruses and bacteria.

Other methods

• UV light: clear water only. Filter cloudy water first and follow the unit’s instructions.
• Sun: clear plastic bottles of clear water on their sides in full sun for 6 hours, or 2 days if it is cloudy.