So continuing on our water conservation theme, let's check the house for water leaks. It's super-easy (and loads of fun) to do:
At night, place an empty cup under each sink faucet and go to bed. In the morning, if there's any water in the cup, you'll know there's a leak. The same system works for the tubs. Most shower heads don't need to be checked since they're generally tub/shower combos and the water won't even go up to the shower head unless the pulley-uppey thing on the tub faucet is up (sorry to go all technical plumber jargon on you there). However, if you have a separate shower unit, place a dry bucket on the floor directly under the shower head.
Toilets are another matter altogether. Mostly, because they're more fun to check. First, remove the tank off the back of the toilet and squeeze in a couple drops of red food coloring. Then leave it be for 20 minutes or so. When you come back, if the water in the bowl is red, you know there's a leak. That, or someone in your house needs some medical attention stat.
So go do some green super-sleuthing and see what you can find. Then we'll worry about how to fix them!