Toilet maintenance stops more than faucet leaks as obvious costs to the water bill, drip, drip, drip . . . penny, penny, penny, no wonder that bill gets so high $$.
But you have a high water bill and you can’t see any leaks. You might not even hear a leak. Go in the bathroom, take the stuff off the top of the toilet tank, remove the lid and place it in a safe place. Look in the tank and check the water level in relation to the overflow tube. The overflow tube is about 10-inches tall and one-inch round in the middle of the tank. Is the water level up to the top of the overflow tube? If it is, then the ballcock must need repair or replacement.
The ballcock is that tall piece on the left with the float attached. To stop the leak, shut off the water and remove the uppermost part, or parts, of the ballcock. You’ll find a gasket in the center that does most of the work in shutting off the water. This part and the gasket should go with you to the store to get replaced.
Better hardware and plumbing shops will have parts and in-store training to repair most ballcocks. Of course they’ll be happy to sell you a new ballcock to replace an obsolete model. My biggest complaint is when folks replace a repairable premium ballcock with a cheepo plastic one because they will just be back in less than a year to replace it again.
What if the water level is below the top of the overflow tube? The water is leaking out of the tank somehow. To test, pour some food coloring in the tank and wait 20 minutes. If the water in the bowl shows color the flush valve is leaking. To repair, remove the flapper or rubber ball at the bottom of the tank and replace it. They could need replacing every five or so years. More often if you put those auto-toilet cleaners in the tank. The bleach pickles the rubber in most flush valves.
Flappers and rubber balls are the most common flush valves. If you have something different, a little investigation may expose what holds water in your tank. If you can’t get the unit off, call your local plumbing or hardware store and describe your mechanism to the clerk. They may help prevent you from breaking something that could be easy to disassemble. Then it’s off to the store to get replacement parts. You may only need one trip if you remember to take the old parts with you.