You may want to be cautious in using gray water on garden plants, especially those intended for food. Depending on the concentration and toxicity of the soap and other compounds in the household water, it may have a detrimental effect on the plant's oils/lipids and the beneficial microbes that help to keep it healthy. That being said, if you're in a severe drought of record this may be your best option.

You can also run the water through a raised rain barrel full of various soil grades with some hearty reed plants grown on top. These will act as a bio-buffer to improve the water quality before it passes into a collection vessel underneath. I guess it depends on how much time/effort/money/craftsmanship you feel like putting into it.