Is it all right to use bath water to water the garden?
There will be standard toilet soap and human being.
This is what is called gray water and has been used for watering since long before indoor plumbing. I think the key is to use very plain organic (no chemicals) soap like Castile or glycerin. Shampoo is another issue and I'd be hesitant there. I also would not spray plants with the gray water but use it to water the soil. Here is more info: https://www.gardeningknowhow.com/garden-how-to/watering/using-graywater-in-gardens.htm