A leaking toilet isn't that much of an issue for some people. But if you have kids at home who are so fond of playing inside the bathroom, you'll have to fix that leak ASAP. You surely do not want any of them to slip and get injured because of the wet flooring, right?! Anyway, I know you wouldn't want to see your utility bill skyrocket, too! Luckily, you just need some good plumbing tools, an adequate supply of DIY skills and a bucket full of patience to fix this problem. Here's a short guide to help you out!
1. Remove the lid of the toilet tank and check the inside. Is the water level already above the overflow tube? If it is, the problem must be with the inlet valve located on the ballcock or the float. To inspect the inlet valve, simply flush the toilet. As the water in the bowl rises, lift the rod that supports the float. If the water stops, the inlet valve is still in good condition. This test will confirm that there's an issue with the float. Configure it to a point that it's level to the water inside the tank. If you're unsuccessful, there may be a problem with the very float. It could have holes or it's simply damaged. If that's case, you'll need to replace it.
3. Now in the event that you tested the inlet valve the water didn't stop from flowing, there should be a problem with the ballcock. I wouldn't advise you to repair it. Instead, I suggest having the whole assembly replaced.
4. When replacing the toilet assembly, you'll have to drain the water from the tank first. Simply flush the toilet and keep on holding the flush lever to dispose most of the water. Use a sponge to remove the excess.
5. Disconnect the water supply line that's attached to the ballcock, right at the base of the tank. You can use a pair of slip-joint pliers to detach the nut that's securing the ballcock to the toilet tank. Lift the assembly. Position the new one into place. Make sure that you'll thread the new nut that's supposed to be placed underneath the toilet tank. Use your pliers again to tighten the connection. Re-connect the water supply line; install the new refill tube and turn the water supply on.
6. If any of the solutions above doesn't get rid of the leakage, you must also check the flapper. Simply turn the supply line again and observe if the water inside the tank will lessen. If it does after approximately 15 minutes, you should loosen the flapper's chain a bit. This will allow the part to drop to position and prevent the leak.
7. If you have already done Step no. 6 and the flapper didn't budge, you have to replace it. Drain the toilet tank of water. Turn the water supply once again and flush the toilet while holding the lever down. Get a clean rag and wipe the flapper's seat, making sure that sediments are removed. Inspect for any signs of cracks. Pull the old flapper and replace it. Turn the water supply on and test the toilet again.