Flow into the toilet is controlled by a float level controller; either a ball-cock on an arm, or more likely the vertical float on a flushmaster type fill valve. The floats can be adjusted to stop water flow when the water rises to the fill line. Yours is not stopping water flow and it goes through the overflow tube into the toilet bowl and out the drain. As far as water use, its like running a faucet 24-hours per day.

Since you probably replaced the valves recently, you should refer to the packaging directions for fill level adjustment. If you can’t locate it, post back and let us know what type valve you used and we can probably describe an adjustment procedure; or you could go look at a package at the store.