Since water is scarce here, I would like to water my pots with used water. I guess that it is not a good idea to use water with soap, but what about water with food remnants? For example, I washed the trays of my food dehydrator with water only. The water is now full of vegetable remnants and no soap. Is it safe to give this water to my plants?
If the greywater is from food preparation, it's fine to use if it doesn't contain salt, oil, or big pieces of food. I'd use a strainer, to get all the pieces. I think the water from the food dehydrator is fine, if it was used only for plant matter, not animal.
So no animal, no salt, no oil, and I'd say if you were baking in the kitchen, don't use rinse water from the dry mix bowl or the wet one. both of these will contain too much material for good health, and possibly even are unsuitable (baking soda/powder, eggs, so on would be bad).
Don't use it if you can't clearly see through it, you want it to be as clear as possible. If you have some that is too concentrated, mix it with more clean water, until it is clear enough to see through properly.