If you live off grid, you are still going to want hot water for showering, bathing, and cleaning around the home. There are quite a few different options for hot water that you can consider using if you want to do this type of project.
I remember the longest hike I ever took, 13 days alone in the wilds in New Zealand without a shower or bath. I'm sure I smelled a bit as I returned towards civilization, and a farmer at a ranch the last night before I reached the nearest town invited me to spend the night under a roof instead of in my tent. I didn't understand at first why he started building a large fire as it wasn't that cold. It was to warm well water so that I could take a warm bath and clean up.
First of all, you need a clean water supply. Many use well water as I did in New Zealand, rain water, or other options like a local pond or creek to get water. This water will need to be run to your hot water heater which can be a variety of things.
The most common option is a commercial hot water heater. There are heaters like this that run independent of the electrical system with their own solar panels that will collect the energy needed to heat the water. This is the most expensive option but gives you the most control over the temperature of the water.
Some choose to have passive solar hot water systems. The most primitive method is to leave out a few hundred feet of black hose exposed to the sun. The water inside the hose will heat up during the day and become extremely hot. Hook this up to the hot water portion of your shower to mix with the cool water. Whatever you do, do not take a shower just from this hose as it will be too hot most of the time.
Some build passive solar systems that are in a box. This can be made with hose or even copper tubing. Some run these around a radiator or use the same mechanics. These will capture the sun's heat and heat the water. There are a variety of plans for these online that you can lookup and duplicate.
What is nice about each of these options is that you are using the sun as opposed to hooked up utilities to take care of your hot water needs.