Depends on what you are growing and how you water...What is better to water your plants with--- rainwater or gray water?
The logic behind that is questionable - I wouldn't eat the poop used for fertilizer or make stew with it either, but I use it in the garden. Not trying to stir up anything, just "thinking" out loud.If your eating what the plants produce, go with the rain water.
If your in that type of climate where every drop of water makes a difference, let the gray water run thru some basic filter system.
You wouldn't drink gray water or cook food in it, so why feed gray water in its raw form to your plants that are producing food for you.