GFX Gravity Film heat eXchanger to recover the heat from waste water
There are lots of ways to heat water more efficiently. They can all be helped by a product like this. I live in the northeast so this works well for me it replaces a short section of the drainpipe in the basement. This recovers more than half the heat from hot water.
wraped around copper drain pipe, copper conducts much better then plastic, most hard ware stores can get any size of copper you want up to 6" acrose, get a chunk of that, wrap it with soft copper tubing, insulate the whole thing, and replace a chunk of your drain pipe, as close to the shower as possible, connecting it is easy if you use those clamp on rubber splice boots.
then to connect the soft copper to the input side of your hot water heater, so the water going in, insted of being cold is warm, you don't really want to replace the cold water going to your shower head with hot water as well, or the longer you shower, the hotter the water will get, and you can get burned, and if the hot water in your water heater is being replaced with warm water, it will take longer to run out of hot water, so your water heater will remain off longer.
We?ve got one of the GFX units. I didn't want to try to make one myself. All I can say is WOW. This is one of the few things my wife was glad I bought (solar panels, inverters, heat recover units). Now she can take a shower forever and never run out of hot water. When I take a shower the water heater might kick on but will actually shut off while I am taking a shower, and we only have a 30,000 btu gas heater. The unit will take our well water from 55F to 75F and the unit is plumbed to the cold water side so even the cold on the shower is already up to 75F so you don't need to set the water as warm to get the correct temp.