Video of a man with brains, a simple, cheap way to have a solar shower while living in a van.
This video is hot, smart, efficient, and intelligent, this is how solar was meant to be, not all the bells and whistle, just sustainable and cheap.
This person has made this more complicated than needed in my opinion, gravity flow would work. Plus if the tube is half full, it would make a huge water flow problem, however, in principal, he is on the right track. I am thinking about having three ways to heat water. Two gallons on top of a propane stove, 110 Hot Water element in a bucket, and a concentric circle of black PVC on the roof... And, 4-5 one liter bottle on top of the roof.
Do you want the plans?
After a surf or paddle in a cold body of water, what a perfect device to have on the roof racks with the boards or boats. Nobody I've seen uses a small capacity solar bladders, but I think you could sell thousands of these on the W. and E. Coasts to kayakers and surfers. The comforts of a 8 or 10 min. warm shower are never more appreciated than when you've been in the cold water for hours.