Jim,
I recently learned about a water purification system that is being promoted by Rotary International for Third World areas without safe drinking water. Simply put: fill a plastic bottle with water, and leave it in the bright sun for six hours. The ultraviolet (UV) light kills the pathogens, and the water is safe to drink. [JWR Adds: This method only works well with fairly clear water. UV light cannot penetrate very murky water, and it will not sterilize any plant matter suspended in the water. So be sure to use a pre-filter when treating water from open sources such as ponds, lakes, or streams. ]
Sound too good to be true? The Swiss-developed system has been saving lives for 17 years. It is fastest in the tropics, where increased water temperature assists the process. Winter use in temperate zones may want to consider using solar ovens or greenhouses to achieve adequate water temperature. Even in bright cloudy weather, the process is effective after two days.
I might not want to make this my first potion, but if stranded in the wilderness, of stuck for an extended period without a reliable water supply, I’d give it serious consideration. Regards, – Ben