Here it is: we turn off the water heater. That's it! We find the breaker switch for the water heater and always have it turned off. When we're going to run the dishwasher or take showers, we turn it on about a half hour before, sometimes earlier in the winter and I've turned it on only about ten minutes earlier in the summer! It keeps the water heater from heating and reheating water that we're only going to use a small amount of. Even if you forget to turn it off (which you may in the beginning!), and leave it on for hours, or even a whole day, that's still 1/30th or less of what the normal usage is!
My husband said that his family grew up doing that and I had never ever heard of it! And even now, when I read articles about being eco-friendly, they'll recommend replacing your water heater, but no one suggests just having it off.
Any unusual ideas you have for responsible environmentalism?