Here was the answer she received: I'm sure with a large family you fill the dishwasher to the brim, but if you can cut back on the number of times you run it by only washing very dirty dishes in the machine and doing the others by hand, that will save water.
Actually, that answer is -- ahem -- not correct.
Surprise! Dishwashers are more efficient than washing dishes by hand! Studies show that even when people are very careful, washing by hand is more wasteful.
That's one reason why I'm stoked that my new landlord just put in a brand-new Energy Star-rated dishwasher! New dishwashers are even more efficient than old models, increasing the benefits of using a washer rather than washing by hand.
It's been about five years since I've lived in a place with a dishwasher, and for the last two or three I've known that dishwashers are more efficient than hand washing. Every time I washed the dishes during that time, I've felt annoyed that what I was doing was both harder on me AND the environment.
But no more. I'm now helping the environment and don't have dishes piling up in the sink because I'm too lazy to wash them. It's a win-win. Don't you love those?