On demand hot water, to replace regular 6 gal tank unit

I was checking out on demand that could be hooked up to campsite water. I found an Eco temp. It has pretty good ratings from owners. There are higher capacity. Also, if camping on a river or lake a pump (with filter) could also provide the water to the heater. I also heard of some shower heads that provide a good output with very little water. Forget the name, but it was discussed on a B conversion group on this list.