The toilet is the biggest business water bandit; the average toilet uses 4 to 7 gallons per flush! Low volume toilets, which can easily replace your old inefficient toilet, will save over five gallons per use. If you cannot replace your toilet just yet, you should at least verify that it is working properly. You can easily check it for leaks by placing a drop of food coloring in the tank. If color shows up in the bowl without flushing, the toilet has a leak.