Brief description

A device that uses solar energy to purify water. It evaporates impure water and collects the pure condensate, effectively removing salts, heavy metals, and pathogens.

Use / Function

• Primary use: Producing potable water from salt water or contaminated sources.
• Secondary uses: Desalination, recovery of water from soil or plants in survival situations.
• Scale: Domestic / Individual.

Operating principle

The solar still replicates the natural water cycle (evaporation and condensation) on a small scale.

1. Evaporation: Solar radiation passes through a transparent cover and heats the impure water in a basin. The water turns into vapor, leaving impurities (salts, bacteria, etc.) behind.
2. Condensation: The vapor rises and touches the cooler underside of the transparent cover, where it condenses back into liquid droplets.
3. Collection: Due to the slope of the cover, the droplets trickle down into a separate, clean collection container.

How to create it

Minimum functional version (Basin Type)

1. Basin: A shallow container or pit lined with a dark, waterproof material (like Clay or black Plastic) to hold the impure water.
2. Cover: A sheet of Glass or Plastic placed over the basin at an angle.
3. Collection Trough: A clean channel or small container placed at the lowest point of the cover’s slope.
4. Seal: Ensure the edges are airtight to prevent vapor from escaping.

Technical level

Basic. Can be constructed with improvised materials.

Materials needed

• Essential materials:
  • Transparent cover: Glass or Plastic film.
  • Waterproof liner: Clay, Stone basin, or plastic sheet.
  • Collection container: Any clean Container.
• Tools:
  • Shovel (if digging a pit), basic cutting tools.
• Substitutes:
  • A hole in the ground with green vegetation can serve as the “impure water” source in emergencies.

Variants and improvements

• Pit Still: A survival version dug into the ground, using soil moisture or added vegetation.
• Wick Still: Uses a dark cloth to increase the surface area of evaporation.
• Multi-effect Still: Reuses the latent heat of condensation to power further evaporation stages, increasing efficiency.

Limits and risks

• Output: Relatively low production rate (usually 1-4 liters per day depending on size and sun).
• Sunlight: Dependent on clear skies and strong solar radiation.
• Contamination: If the collection container is not kept clean, the purified water can become re-contaminated.
• Volatile compounds: Some chemicals with boiling points lower than water may evaporate and condense along with the water.