There are several answers to this question.   as sustainability project that aims to be toxic chemical free, the question of how to keep the water clean without nasties was frying our brains a bit too much.  Plus the power usage is a bit crazy.  We are also surrounded by mountain woodland so not allowed to have fires in the hot dry months, so even a wood fired hot tub is out of the question. I’m just not that into them. personally, I get a bit icky about floating around in a tub with others peoples dirt particles!