Water
Solar Water Disinfection Using PET Bottles (SODIS)
The SODIS method (Solar Water Disinfection) is a simple, effective technique for purifying water using only sunlight and clear plastic bottles. UV-A radiation from the sun, combined with heat, penetrates the water and destroys pathogenic microorganisms like bacteria, viruses, and parasites. This process makes contaminated water safe to drink without the need for electricity, fuel, or chemical additives. It's particularly useful in remote areas or emergency situations where other purification methods are impractical or resources are scarce. The principle relies on exposing water to sufficient sunlight for a specified duration, typically several hours.
Topic summary
The SODIS method (Solar Water Disinfection) is a simple, effective technique for purifying water using only sunlight and clear plastic bottles. UV-A radiation from the sun, combined with heat, penetrates the water and destroys pathogenic microorganisms like bacteria, viruses, and parasites. This process makes contaminated water safe to drink without the need for electricity, fuel, or chemical additives. It's particularly useful in remote areas or emergency situations where other purification methods are impractical or resources are scarce. The principle relies on exposing water to sufficient sunlight for a specified duration, typically several hours.
Key takeaways
- The sun is visible and directly hitting the bottles (for clear days).
- Water in bottles reaches a noticeably warmer temperature.
- The clarity of the water remains consistent post-treatment (SODIS does not remove turbidity).
- No new sediment or organic growth appears in the treated water.
- Avoid: Using opaque or colored bottles, which block UV light.
- Avoid: Not removing labels or adhesive, reducing sun exposure.
Intended uses
- Water skill (Beginner, ~5 min practice)
- Requires: clear PET plastic bottles (1-2 liter), dark colored surface (e.g., tarp, rock, roof)
Climate suitability
Any outdoor environment with direct sunlight; ideal for remote settings, camping, or emergency preparedness lacking access to conventional purification.
Verification notes
Author: Wild10 Editors. Last updated September 15, 2026.
Required tools
- clear PET plastic bottles (1-2 liter)
- dark colored surface (e.g., tarp, rock, roof)
Required materials
- water suspected of contamination
Step-by-step
Obtain clear, label-free PET plastic bottles (1-2 liter size are optimal).
Why: Clear PET bottles allow UV-A rays to penetrate effectively; labels block sunlight.
Rinse bottles and remove all labels and adhesive for maximum sun exposure.
Why: Any residue will hinder light penetration and may leach into the water.
Fill bottles no more than three-quarters full with low-turbidity water.
Why: Partial filling allows for air incorporation during shaking, increasing oxygen.
Shake the bottle vigorously for 20-30 seconds to oxygenate the water.
Why: Oxygenation assists the UV-A radiation in inactivating pathogens.
Top off the bottle with more low-turbidity water, leaving a small air gap.
Why: Filling completely ensures maximum water treatment volume.
Place bottles horizontally in direct sunlight on a dark, heat-absorbing surface.
Why: Horizontal placement maximizes surface area exposure to sunlight; dark surfaces increase water temperature, enhancing purification.
Leave bottles undisturbed for a minimum of six hours on a clear, sunny day or two consecutive days if overcast.
Why: Sufficient exposure time is critical for the UV-A rays and heat to effectively neutralize harmful microorganisms.
Tip: Orient bottles East-West to maximize direct sun exposure throughout a full day.
Common mistakes
- Using opaque or colored bottles, which block UV light.
- Not removing labels or adhesive, reducing sun exposure.
- Treating highly turbid or cloudy water, which prevents UV penetration.
- Insufficient sun exposure time, leading to incomplete purification.
- Placing bottles in shade or on light-colored surfaces.
Troubleshooting
- If water is cloudy, pre-filter it through cloth or allow sediment to settle before SODIS.
- If direct sunlight is intermittent, extend treatment time.
- Elevate bottles slightly off the ground to prevent them from being submerged in pooling water.
- Confirm bottles are made of PET by checking the recycling symbol (number 1).
Field practice drill
Practice by treating a batch of tap water for the full duration and observe the clarity and temperature change.
Indicators of success
- The sun is visible and directly hitting the bottles (for clear days).
- Water in bottles reaches a noticeably warmer temperature.
- The clarity of the water remains consistent post-treatment (SODIS does not remove turbidity).
- No new sediment or organic growth appears in the treated water.
Related outdoor skills
Educational reference only. Wilderness conditions change fast — practice in low-stakes settings, take a certified wilderness first-aid course, and confirm regional regulations before you rely on any of these skills in the field.