A major source of water for reuse comes from our kitchen sink in part because we constantly eat lots of vegetables and fruits that need to be rinsed. Try to use water at least twice, and if safe, three times- or more if you are clever. Experiment. We have three containers, two in the sink. One is for water that isn’t soapy or too greasy or salty- safe for the bird bath or the garden plants. The other is for water that is less pure, yet this can be used for trees. I water my entire garden of an apple tree, asparagus, grapes, rhubarb and more just from kitchen sink water. 
These containers also supply water to use for other things like wetting a rag to wipe the floors or soaking dishes before cleaning. This water is also carried to the bathroom and used for flushing sometimes. The third container is for compost- no food wastes ever go into the trash. We allow this to have a lot of water in it as well, and then either dump it into the compost pile or do some sheet composting around the ground below the tree. We have not used a garden hose in many years despite our dry climate.