Frequently Asked Questions Leaky Toilets? Expand Here is a way to figure out if your toilet is wasting water: Add food coloring to the back of the tank and let it sit for 5 minutes, then check the bowl to see if any color has appeared. If so it is time to replace the flapper valve. A leaky toilet can leak up to 2500 gallons per day. Average family of 4 uses uses 260 gallons of water per day.