So, I'll tell you this water heater works. It's essentially like a small heating system mounted on a wall. It has 200,000 BTU's of heat that make water real hot, real fast. So, if you are going to shower, there's going to be plenty of water.
If everybody on your street wants to shower, there's going to plenty of hot water. It's a very good system that recovers very quickly, so if you tend to take long showers, you'll have plenty of hot water; short ones, the same thing. Tankless water heaters work by a large flame in a small box heating water, extremely fast.