Solar Water Disinfection (SODIS)¶
Disinfection & Chlorination • Est. CapEx: $2.50 USD • Lifespan: 7–15 Years
Technical Overview¶
A simple, low-cost method that uses sunlight to kill pathogens in water. Suitable for households in developing regions with limited access to clean water.
Key Specifications & Engineering Parameters¶
| Parameter | Specification |
|---|---|
| Category | Disinfection & Chlorination |
| Capital Cost (CapEx) | $2.50 USD |
| Power / Energy | Solar PV / Thermal |
| Target Scale | Household (5–10 people) |
| Standard Lifespan | 1–3 Years (bottle UV degradation) |
| Technology Maturity | Commercially Available / Open Source (WHO / Swiss Eawag) |
| Primary Mechanism | Clear, transparent PET (#1) bottles filled with low-turbidity water (<30 NTU) are aerated by vigorous shaking and exposed horizontally to direct solar radiation for a minimum of 6 continuous hours (or 2 full days under overcast skies). UV-A radiation and thermal heating (>50°C) act synergistically to destroy pathogen DNA/RNA and generate reactive oxygen species. |
Engineering Trade-Offs¶
- Zero Consumable/Operating Cost: Requires zero fuel (firewood/charcoal), electricity, or recurring chemical consumables (chlorine tablets).
- Effective Pathogen Kill: Achieves 99.9% inactivation of vegetative bacteria (E. coli, Vibrio cholerae, Salmonella), viruses (rotavirus), and protozoan cysts (Giardia, Cryptosporidium).
- Safe Sealed Storage: Drinking directly from or storing water within the sealed PET bottle eliminates secondary hand/cup recontamination.
- Simple Household Operation: Minimal training required; can be managed at the household level using locally collected 1.5L–2.0L transparent bottles.
- Turbidity Vulnerability (<30 NTU Limit): Suspended silt, clay, and tannins absorb and scatter UV-A rays, preventing disinfection. Requires settling or pre-filtration if water is cloudy.
- Ineffective Against Chemical Toxins: Completely ineffective against dissolved chemicals, heavy metals (arsenic, lead), fluoride, and salinity.
- Weather Dependent: Highly unreliable during rainy seasons or prolonged overcast cloud cover; requires 2 consecutive days if cloud cover exceeds 50%.
- Volumetric Bottleneck: Limited to 1.5L–2.0L per container (max 10 cm water depth). Treating 40–80 liters daily for a household requires managing 20–30 separate bottles on roofs.
- Thermal / Taste Acceptability: Water heated on metal roofs reaches 45–55°C, resulting in flat, warm water with potential plastic taste if lower-grade containers are used.
Swiss Eawag Standard Operating Protocol¶
1. Bottle Selection: Use clean, transparent PET (#1) bottles (max 2.0L / 10cm depth). Avoid PVC (#3), tinted plastic, or heavily scratched bottles.
2. Turbidity Test: Place filled bottle over a newspaper headline. If you cannot read the print looking down through the neck, pre-filter or settle first.
3. Aeration: Fill 3/4 full, cap tightly, and shake vigorously for 20–30 seconds to dissolve atmospheric oxygen (essential for reactive oxygen species formation). Top off completely.
4. Solar Exposure: Place horizontally on a reflective surface (e.g. corrugated galvanized iron roof). Expose to full sun for at least 6 continuous hours (or 2 full days if overcast).
5. Safe Use: Keep capped until drinking. Do not touch the bottle lip or pour into unwashed cups.
Cross-Reference & Interactive Tools¶
Need to evaluate this technology for your specific field site? Run the WhatWater.info Selector Engine to compare it against 100+ alternative solutions.