Iodine Water Purification Calculator
Calculate iodine drops needed per liter to purify drinking water.
Adjusts for water clarity and temperature with required contact time for disinfection.
The standard dose is 5 drops of 2% iodine tincture per liter of clear water. That gets you to roughly 8 ppm iodine — enough to kill bacteria, viruses, and most protozoa with a 30-minute contact time at room temperature.
Cloudy water needs more iodine. Suspended particles consume some of the dose before it reaches pathogens. Double the drops for visibly cloudy water, then let it sit longer.
Cold water needs longer contact time. Iodine is a chemical reaction, and cold slows reactions. Below 5°C / 40°F, doubling contact time (60 minutes) is the standard recommendation. Some sources say to warm the water first if possible.
What iodine kills.
- Bacteria (E. coli, Salmonella, Shigella): yes, fast
- Viruses (Hepatitis A, Norovirus): yes
- Giardia cysts: yes, but needs full contact time
- Cryptosporidium oocysts: NO — iodine does not reliably kill Crypto. Use a filter or boil for Crypto-suspect water.
Iodine forms.
- 2% tincture: most common, the calculator default
- 10% povidone-iodine: 5x weaker per drop than 2% tincture in disinfection terms (most of the dose is bound)
- Iodine tablets (Polar Pure, Potable Aqua): pre-dosed, follow package
- Lugol’s solution (5% iodine): half the drops of 2% tincture
The taste problem. Iodine-treated water tastes medicinal. A pinch of vitamin C added AFTER the contact time neutralizes residual iodine and removes the taste. Do not add C before the wait period — it cancels the disinfection.
Long-term use warnings. Iodine treatment is for emergency or short-term use. Pregnant women, people with thyroid conditions, and anyone allergic to iodine should not use it. Long-term consumption (over a few weeks) of iodine-treated water can affect thyroid function. For multi-month use, switch to filtration or chlorine-based methods.
Worked example. 1.5 L of cloudy water at 50°F.
- Base dose: 5 drops/L × 1.5 L = 7.5 drops, round to 8
- Cloudy water: double to 15 drops
- Cold water adjustment: extend to 45 minutes contact
Add 16 drops, swirl, wait 45 minutes. Add a pinch of vitamin C just before drinking if you want to kill the taste.