How do you confront others about their green missteps (and your pet peeves)?

Everyone has a

For example, when I was a little girl, I used to see a family member (they shall remain nameless) leave the water faucet on while doing the dishes. She or he would start to wash a dish, walk away to do something else, and then come back. I didn't understand why they didn't just turn the water off if they were going to step away for 15-20 seconds at a time? It seemed like such a huge waste of water even at a young age when the words "green" didn't really mean much to me.