We haven't implemented any serious efforts at outside rainwater diversion (yet), but in the house, I have tried a few strategies for saving and re-using waste water. Here is a picture of a bucket I'm using in the kitchen to catch pasta water and other kitchen water. For those who were fans of Tony's Pee Week, THIS IS NOT A PICTURE OF PEE.
After it cools, I imagine the plants will like it because of the extra nutrients in there.
UPDATE: after making beet lipstick (see posting later this week) the water is now a lovely shade of pink!