Water Purification Dosages & Boil Times

Chlorine (Unscented Household Bleach) Dosages

Strength varies by product; check label.

• 6% sodium hypochlorite
  • Clear water: 2 drops per liter (8 drops/gal); wait 30 min
  • Cloudy water: 4 drops per liter (16 drops/gal); wait 30–60 min
• 8.25% sodium hypochlorite
  • Clear water: 1–2 drops per liter (6 drops/gal); wait 30 min
  • Cloudy water: 3–4 drops per liter (12–16 drops/gal); wait 30–60 min

Slight chlorine smell should be present; if not, repeat dose and wait 15 more minutes.

Iodine Dosages

2% tincture (guideline; follow label)

• Clear water: ~5 drops/L; 30 min contact
• Cloudy/cold: Double dose and/or 60 min

Avoid in pregnancy/thyroid disease; less effective for Cryptosporidium.

Boil Durations by Altitude

Bring water to a rolling boil:

• Sea level to 2,000 m / 6,500 ft: 1 minute
• Above 2,000 m / 6,500 ft: 3 minutes

Notes

• Boiling inactivates bacteria, viruses, protozoa; does not remove chemicals.
• Cyanobacteria (blue‑green algae) toxins are not reliably removed by boiling, filtering, or common chemicals—avoid suspect water entirely.

Chlorine Dioxide

• Follow manufacturer instructions (tablet/drop strength varies)
• Effective for bacteria, viruses, Giardia; requires up to 4 hours for Cryptosporidium

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Mark treated vs untreated containers clearly to prevent mixups.

Further Reading

• EPA: Emergency Disinfection of Drinking Water (EPA 816‑F‑15‑003)