There are lots of small changes you can make to conserve water. Here are some tips at 100 Ways to Conserve.
The bathroom has lots of opportunities to save. If you have an older water tank with your toilet, place a plastic bottle filled with rocks in the tank. It will limit the amount of water stored and reduce water used for each flush.
Note: Don't use a brick, which some people recommend, it can disintegrate.
If you think your water is slowly running from the tank, either get the colored tablets from your water department for testing or put a few drops of food coloring in the tank. If it leaches into the water in the bowl, you may need to change out the flapper.