Solar Water Disinfection (SODIS): A Low‑Cost Path to Safe Drinking Water
Solar Water Disinfection, commonly known as SODIS, is a sustainable method recommended by the WHO to purify contaminated water using just PET bottles and sunlight.
How It Works Fill & Clean – Use clear, undamaged PET bottles and remove labels.
Expose to Sunlight – Lay bottles horizontally in direct sunlight for at least 6 hours; extend to 48 hours on cloudy days.
UV + Heat Inactivation – UV-A radiation and thermal effects destroy pathogens by damaging proteins and DNA, rendering microbes unable to recover.
Benefits & Impact Extremely low cost — uses common PET bottles and sunlight
Proven effectiveness in reducing waterborne illnesses like diarrhea
Accessible globally — adopted in over 33 countries, benefitting millions
Limitations Only suitable for low-turbidity water (≤30 NTU); pre-filtration may be needed
Efficiency varies with sunlight intensity, bottle material, and seasonal conditions
Bottle clarity degrades over time — scratches or aging PET reduce UV penetration
Educational Value for Circuit Press SODIS is an excellent student project because it:
Demonstrates science in action — linking solar radiation, microbiology, and chemistry
Shows how simple materials and observation can achieve significant health impact
Encourages citizen science — students can test different exposure times and turbidity effects
Example Student Experiment Measure bacterial levels before and after SODIS exposure using test strips
Compare exposure durations (e.g., 6 hours vs. 48 hours) and bottle orientations (horizontal vs. vertical)
Record observations on water clarity, sunlight conditions, and local impact to strengthen hypothesis testing and analysis skills