Even in the summer months, it's nice to have hot water for the shower, doubly so if you have a spa or hot tub. To help you keep things steamy while keeping your electricity bills down, here's a surprisingly simple DIY project. For about $60 worth of materials, you can make your own water heater, installed on your roof. Here's how.
This project deals with heating a spa, but with some tweaks near the end of the process, you could use it to heat a pool, sink or bathtub.
This project is the work of Instructables user Greg Horejsi, aka petastream. Special thanks to him for his permission to post it here.