Leaking toilets can waste 14,000 gallons of water per day and cost consumers hundreds of dollars a month on their water and sewer bills. To detect a slow leak, put food coloring in the toilet tank and wait up to 12 hours without flushing. If the water in the bowl turns color, your toilet tank is leaking. Replace the parts inside your toilet tank. Repair kits are inexpensive and are available at most home improvement stores.