Thought this is a pretty interesting concept to be developed further. Also there's always a part of me that is made quite happy in the knowledge that sunlight purifies water. (Though usually not so quickly as this!)
http://www.iflscience.com/technology/student-develops-inexpensive-solar-lens-purify-polluted-water
http://www.iflscience.com/technology/student-develops-inexpensive-solar-lens-purify-polluted-water