Bad Flapper: If you had water run into the bowl during the dye test and the water level is not set too high, your flapper is probably leaking and it should be replaced. If your old flapper has a float on the chain, make sure your new one does too (or put the old float on the new chain).
Fill Valve Problem: If you can’t adjust the water level lower or can’t get the fill valve to shut off, replace the fill valve. Pedestal fill valves are considered more reliable than the ball and float type.
Flushing Mechanism: Occasionally the entire flushing mechanism will need to be replaced. Call a plumber if you need help. If you are a do-it-yourselfer and want a little guidance, check out Toiletology. There you will find a wealth of information for fixing, replacing, adjusting and cleaning toilets.
Hot Water Tanks: It’s pretty hard to miss when a hot water tank goes bad, but it is a good idea to check around the tank for any small leaks. This can prevent the major flood that occurs when the tank gives out.
Sinks, Bathtubs, Dishwashers, etc.: Make a habit of checking under sinks, around the shower and bathtub molding, and along the bottom front edge of the dishwasher for any unusual damp spots. If a leak is found, plumbing supplies can be purchased at your local home improvement center, or you can contact a plumber for help.
Toilet Tanks: The most common indoor leaks occur in the toilet tank. Many toilet leaks are silent, but if you hear your toilet running, or flushing when no one has touched the handle, you have a toilet leak. You can check for a leaking toilet by removing the tank lid and putting 5 to 10 drops of food color in the tank. Put the lid back on but don’t flush it yet. After about 10 minutes, look in the bowl. If you see color in the water, you have a leak. The main causes of a toilet leak are either a "fill valve" that will not shut off or a bad "flapper".
Washing Machine Hoses: It is a good idea to check behind your washer to be sure there is no water dripping from a worn washing machine hose. If you find any water dripping, new hoses can be purchased from your local home improvement center.