BUCKHORN CLIFFSA preparedness field manual

Water · Formula · Book recipe 6.3

Purify Water with Lugol's Iodine (2%)

When filters break and boiling isn't possible, a few drops of Lugol's solution can make questionable water safe to drink.

Handle with careWorks without power

How it works

Pre-filterclear water through cloth
5 drops / quartdouble if cold or cloudy
Wait 30 min60 min if cold or cloudy
Safe to drink~5-10 ppm iodine
Add taste fixes after the waitascorbic acid, baking soda, or lemon
Will not kill Cryptosporidiumboil or 1-micron filter if that's a risk

Quick facts

  • Clear water5 drops / quart
  • Cloudy/cold10 drops / quart
  • Per gallon20-40 drops
  • Wait30-60 min
  • Use3-4 weeks max

Hazard

Short-term emergency use only. Avoid with iodine allergy; limit with thyroid disease or pregnancy. Does not kill Cryptosporidium.

Lugol's is light and portable; sealed bottles stay effective for years. Iodine quickly kills bacteria and viruses, and inactivates Giardia cysts given enough contact time (see Step 3). It does not kill Cryptosporidium; pre-filter through a 1-micron filter first if that is a risk. The drop counts below follow EPA's emergency-disinfection guidance and standard wilderness-medicine practice, giving about 5 ppm free iodine in clear water and roughly double that in cloudy or cold water, within accepted ranges for iodine disinfection.

What you'll need

  • Lugol's Iodine Solution (2%) in amber dropper bottle
  • Water that is clear (pre-filtered or settled if possible)
  • Clean mixing container
  • Optional: ascorbic acid powder, baking soda, or lemon juice to improve taste after treatment

Steps

  1. Pre-filter cloudy or murky water through a clean cloth, or a bottle filter (Recipe 7.3), to remove sediment and debris. The cleaner the water going in, the more effective the iodine treatment.
  2. Add 5 drops of 2% Lugol's per quart or liter of water (about 5 ppm free iodine), or 20 drops per gallon. For cloudy water or water below 60°F, double to 10 drops per quart or 40 drops per gallon. If your bottle is 5% Lugol's instead, use 2 drops per quart for clear water or 4 for cloudy. Stir well to distribute evenly.
  3. Wait at least 30 minutes before drinking; for cold or cloudy water, wait 60 minutes, and longer for near-freezing water. A faint yellow or brown tint shows iodine is present but is not a standard residual test; rely on the full contact time, not color.
  4. To improve taste after the full wait time has passed, add a few crystals of ascorbic acid powder (only a tiny amount is needed), a small pinch of baking soda, or a squeeze of lemon juice. Do not add these before the wait time as they can interfere with the iodine before it finishes working.

Warnings

Use only for short-term emergencies, no more than about 3 to 4 weeks. For infants, young children, pregnant or breastfeeding women, or anyone with thyroid disease, use boiling or bleach instead whenever possible; avoid iodine entirely with a known iodine allergy. Iodine will not kill Cryptosporidium; boil or filter if that is a risk. Do not exceed the recommended doses, and confirm your bottle's strength before dosing.

Storage and shelf life

Unopened: 5 to 10 years in cool, dark, sealed conditions. After opening: shelf life varies by storage and manufacturer (commonly 12-18 months); replace if color fades, crystals form, or potency drops. Best container: amber glass, tightly sealed; HDPE plastic is acceptable. Avoid clear glass and reactive metals (aluminum, copper, plain steel). See the Containers section.

Questions this answers

Tap a question for the short answer.

How many drops of lugol's iodine purify a liter of water?

Add 5 drops of 2% Lugol's per liter or quart of clear water, about 5 ppm free iodine. Double to 10 drops for cloudy water or water below 60°F. With a 5% bottle, use 2 drops for clear water or 4 for cloudy. Stir well.

How long do I wait after adding iodine to water?

At least 30 minutes for clear water, and 60 minutes for cold or cloudy water, longer if it's near freezing. Rely on the full contact time, not the yellow or brown tint, and add any taste improvers only after the wait.

Can I purify cloudy water with iodine?

Yes, with extra steps. Pre-filter it through a clean cloth or a bottle filter to remove sediment, double the dose to 10 drops of 2% Lugol's per quart or 40 per gallon, and wait 60 minutes instead of 30.

Does iodine kill giardia and cryptosporidium?

Iodine inactivates Giardia cysts given enough contact time, and it quickly kills bacteria and viruses. It does not kill Cryptosporidium, so pre-filter through a 1-micron filter, or boil, if that is a risk.

Who should not drink iodine treated water?

Infants, young children, pregnant or breastfeeding women, and anyone with thyroid disease should use boiling or bleach instead whenever possible. Anyone with a known iodine allergy should avoid it entirely. For everyone else it's short-term only, no more than about 3 to 4 weeks.

How long does lugol's iodine last?

Unopened, 5 to 10 years in cool, dark, sealed conditions. After opening it varies by storage and manufacturer, commonly 12 to 18 months. Replace it if the color fades, crystals form, or potency drops, and keep it in tightly sealed amber glass.

Keep going

Read nextClean Water: Which Method Makes Which Water SafeWhat is actually in bad water, which treatment handles which problem, the one rule that covers most of it, where the water in your house is hiding when the tap stops, what to store, how to test a well, and the tools I keep.Water · Guide

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Water · FormulaSource: Prepper's Chemical Survival Guide, Recipe 6.3, p. 29 · Last reviewed 2026-09-18

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