This process is also known as solar-oxygen treatment and relies on a combination of UV and oxygenation provided by agitation. You really need either a clear glass or clear plastic PET bottle for it to work well, such as a two-liter soda bottle. A new supply must be treated each day as UV treatment provides no residual anti-microoorganism effect. The process is described in detail in The Ultimate Desert Handbook by Mark Johnson (www.ultimatedeserthandbook.com)