Grey water is waste water in the home, for instance from dish, shower, sink, etc. except from toilets. This may be reused for some purposes, especially landscape irrigation. The benefits of grey water recycling including: lower fresh water use, less energy and chemical use , and groundwater recharge.
People need to be careful. In many parts of the US the use of gray water is illegal. People need to check into any local ordinances. In the places that ban it the fines can be pretty big.
Grey water is another reason to make sure that all the different soaps you use contain no harmful chemicals, since the water is going on your garden, lawn, etc.
We don't do this, but we do "recycle" some water on smaller levels. Like if a glass of water isn't finished and is left out.....or a pot of water was boiled to cook veggies in, etc, then that leftover water gets used to water the plants.
few years back when we were having a water shortage, the use of grey water was widely discussed. It is perfectly ok to use bath water which had soap in it on lawns and plants as it would not harm them..
I remeber one restaurant that only serves water to guest when asked for and if the water is left they do reuse it to clean etc....or water the plants....
We use grey water from the kitchen and bathroom sinks, the shower, and the washing machine. For some reason, the plants love the detergent from the washing machine. There is a clear difference, they are so much greener than the other plants.