Solar water furnace?
 

My son in law asked me if your making a solar furnace to heat air, why can't you use it to heat water. Learning to use solar myself I didn't know how to answer him. It makes since that Aluminum cans with holes in both ends silicone together in a tube should be able to handle water trickling through them. The holes drilled in the ends would cause turbulent and small pools of water to form at the rims, during the flow. Being black sealed in glass or such would provide the heat.

I'm thinking about trying it.

What you think?

Sound like a lot of work, but I don't see why it wouldn't work. Efficiency is anyone's guess. Also, I'd think you'd eventually get bacteria build up in the cans from sitting water and air.