Check out this device invented by an Australian design student in 2011. It's called a Solarball and it's "a personal and portable water purification device, capable of producing potable water out of contaminated water. The device can produce up to 3 litres of clean water daily, by absorbing heat from the sun, causing dirty water contained inside to evaporate. As evaporation occurs, contaminants are separated from the water - generating drinkable condensation. Might be something for the BOL--have a couple or three. Jon Liow | Industrial Design
You may also find this useful Banana peels can be used to purify water This is both life raft and solar still, and claims to provide drinking water for five adults daily. The SeaKettle life raft will make drinking water from the sea