The sight of water on the floor around your toilet usually means there's a leak, and the location of the water is the first clue about the source of the leak. Tank leaks deposit water behind the toilet, while bowl leaks are evident around the front of the toilet. Your toilet also has a leak if the fill valve runs constantly or cycles on and off, even when you don't flush.
Leaks From the Tank
Water leaking from under the tank usually means that the connector for the water supply or one of the tank bolts is loose. Before making any repairs, locate the source of the leak, and if you see water seeping through a crack in the tank, you need a new tank.
To stop water from spraying from the supply connector: Tighten the connector by hand or -- if necessary -- with adjustable pliers. Wrapping plumbing tape around the threads also stops leaks, and you can do this if necessary, but toilet connectors usually don't need it.
To tighten a tank bolt: Hold the head of the bolt steady with a screwdriver while you tighten the nut under the tank with pliers -- you'll probably need a helper, and you can do it while the tank is full.
If you can't stop the leak from the bolt, the washer is worn and needs replacing.
Leaks Around the Bowl
If water is pooling around the bottom of the bowl, you have to remove the toilet to assess the situation. The wax ring may be leaking, and if that's true, you can simply replace it with a new one. Usually, though, the leak is caused by a loose, corroded or poorly installed flange, and you may have to repair the flange or -- if it has been set too high -- shim up the toilet to prevent it from rocking and breaking the wax seal. Flange repair kits are available at any hardware store and are easy to use. As with the tank, any water leaking from a crack is a sign you need a new bowl or toilet.
Leaks Between the Tank and the Bowl
A flapper or canister seal holds water in the tank and prevents it from going into the bowl until you flush. When the flapper or seal leaks and the toilet runs, you can replace either without much difficulty.
To replace a flapper:
Turn off the water and flush the toilet to drain the tank.
Pull the flapper off the overflow tube and disconnect the chain.
Purchase an identical replacement and install it by reversing the procedure for removing it.
For toilets with a canister flush valve:
If your toilet has a canister flush valve, the procedure is similarly uncomplicated.
Shut off the water, flush the toilet and disconnect the flush handle.
Turn the canister counterclockwise to release it, then remove it from the tank.
Pull off the washer from the bottom of the tank or the toilet siphon hole and replace it with a new one.
Reassemble the flush valve.