There are four possible reasons why your toilet is leaking water and you need to act fast to prevent further expensive water bills. In worst case scenario, water could leak out on to your floor which do further damage to your flooring.
Some of the parts of the toilet plumbing system can be bought and replaced and some parts simply are not repairable. In that case, the only option is to get a whole new toilet tank and bowl system. If after all the things you have tried on your own and you still are unable to stop the leak, it is highly advisable as a last resort to call your plumber to fix the toilet leak problem.
1. To test if there is an actual leak happening from your toilet tank to your toilet bowl, put some food coloring into your "Toilet tank water". Wait for about 5 or 10 minutes and watch to see if any of the food coloring seeps into the toilet bowl. Do not flush the water at any time. If there are indeed some food coloring appearing in the toilet bowl standing water, then you know you have a water leak happening.
2. Your fill valve arm may have been positioned at a wrong height causing the water to leak into the overflow pipe. Try adjusting the height of your fill valve arm until the water level stays below the top mouth of the overflow tube. Please note, check to see the refill tubing is attached properly to the tip of the overflow pipe by a clip.
3. Your overflow pipe may be having a crack somewhere. If this is the case, then you may need a new overflow pipe. You can buy this overflow pipe from home hardware store in your local area or online and installation is not so difficult. Please note that this overflow tube comes attached with the flush valve drain system as manufactured. You need to be careful to buy the correct size of the overflow pipe system, usually in 2 inch or 3 inch size.
4. Your flapper seal might be causing the leak, if it doesn't seal close tight back every time you flushed water. It is simple to buy a new flapper seal and replace the old flapper. Look for either 2 inch or 3 inch flapper depending on the size of your flush drain valve.
5. Your flush valve drain is connected to the above mentioned overflow pipe as manufactured. This entire system could be faulty and will need to be replaced with a new one. (2 inch or 3 inch size of the flush drain valve)
6. There is a rubber gasket which creates a seal between the toilet tank and the toilet bowl connection. If this rubber basket is worn out, leak can occur and water will flow into the toilet bowl non stop.
7. There are two toilet tank bolts resting on two rubber washer located inside bottom of the toilet tank. These two toilet tank bolts secure tight the toilet tank and toilet bowl together. If the washer underneath the bolt inside the toilet tank is worn out, you will have water leak flowing out of the water tank onto your floor. Replace the old washer and bolt with new ones.
8. The last possible leak explanation will be the ceramic toilet tank itself has cracks somewhere. If this is the case, you can either buy only the toilet tank and install it or buy am entire toilet tank with toilet bowl. These days it is better to buy the entire toilet system because you may not get only the new toilet tank fitting your old toilet bowl. Besides, the price to buy an entire toilet taNk and bowl will cost somewhat the price of single top toilet tank only.