According to the Environmental Protection Agency, it takes 35 gallons of water to fill the average bathtub. Switch to a five-minute shower with a low-flow showerhead, and you'll save 22.5 gallons each time you scrub up!
According the National Sanitation Foundation, a leaky toilet can waste as much as 500 gallons of water each day! Place a dye tablet (free at home improvement stores) in the toilet tank, and watch to see if the dye seeps into the bowl. If it does, you have a leak that needs to be addressed.
Toilet flappers break down quickly, and should be replaced once a year – even if they say they're good for longer. A couple dollars spent on a replacement flapper will save you much more on your water bill.