Another tip for saving water popped up at
Ecomodder.com: Put a brick in your toilet tank to decrease the amount of water in each flush. Nice read:
EcoModder - Pooping Bricks:)
And here's a controversial tip that the Wife and I practice: We try to pee one right after the other. This allows the first person to not flush, while the second flushes using grey water from washing hands. Saved water = 8-10 liters, 2-4 times a day.