If you open your tank you might see it floating around. You will see in your tank multiple ballcocks, and overflow holes. The one that is still filling the tank, and the water reaches the overflow hole is the problematic one, get a plumber to fix or provide you a new one. If your ballcock is not broken then it is probably too high, this is easily solved by bending the lever arch (metal rod it is on) downwards, this way the ballcock hits the cut off switch before the water reaches the overflow release.





storage tank

To stop your water tank from leaking after an flood, you should know that the float itself does not usually fail, it's typically the closing diaphragm in the ballcock, which is made up of rubber that prevents working.