SODIS: Solar Water Disinfection
WHO-recognized: clear PET bottles in direct sun use UV and heat to reduce pathogens. Water must be clear first.
Question 1
The goal
Disinfect small batches of clear water with sunlight only.
Question 2
Materials
- Clear PET plastic bottles (2 L or smaller)
- Strong sunlight
- Dark or reflective surface
Question 3
Substitutes
- Corrugated metal roof as a reflective surface
- Clear glass is less effective — it blocks more UV
Where to find it
| Material | Household | Wilderness | Urban / scavenged |
|---|---|---|---|
| Clear PET bottle | Soda or water bottles | Bring from pack/trash on trails | Recycling bins |
| Reflective surface | Foil on a baking sheet | Flat sunny rock | Metal roof, car hood |
Question 4
Step by step
- 1
Use only clear, unscratched PET bottles without labels.
- 2
Fill with clear water (you should read newsprint through the bottle).
- 3
Lay bottles flat in full sun on a reflective or dark surface.
- 4
Expose 6 hours in full sun, or 2 consecutive days if cloudy.
- 5
Drink directly from the bottle to avoid recontamination.
Saved steps go to My Survival Notebook.
Question 5
The science
UV-A radiation damages microbial DNA and creates reactive oxygen species; above ~50 °C heat adds a synergistic effect.
Question 6
Dangers & limits
- Ineffective in cloudy water or on rainy days.
- Does nothing against chemicals.
- Not a substitute for boiling when available.
Question 7
How you know it worked
Clear water received the full exposure time in direct sun.