Definitely, in fact you should periodically check your toilets for leaks. Just place a few drops of food coloring in the tank (NOT the bowl). You can also use a few tablespoons of instant coffee or Kool-Aid. In thirty minutes, if the water in the bowl is colored, the tank is leaking and the stopper and valve seal may need to be replaced. At this point, unless you are an expert do-it-yourselfer, call a plumber.