No Stupid Questions

Not sure what you're describing, a toilet lid, neither the seat lid nor the cistern lid, has anything to do with preventing a leak.

So, which lid is this and what is the nature of the leak?

Dad knowledge incoming!

If the heavy ceramic lid of the tank hit and cracked the actual toilet or the tank, the whole toilet needs to be replaced. Sorry. A toilet is $150 for a cheap one, and they aren't hard to replace yourself. Lemmy (hah) know if you want instructions!

Removing the tank (cistern) lid and/or the seat+lid is irrelevant to the function of the toilet. The tank lid is only removable so you can fix the flap and valve if it's ever necessary. The seat lid is to avoid dropping stuff into the bowl and to reduce the spray of germs when flushing.

Where is the leak coming from?

If the water is coming from under the tank (between the tank and the toilet), then either the tank bolts have come loose from people leaning back into the tank, or the rubber seals/washers have gone bad. If the tank wiggles when you push it, the tank bolts are either loose or the washers are crumbling. (It happens)

If the leak is only inside the toilet, you may hear the toilet refilling on its own every few minutes and if you look carefully you may see the trickle of water entering the bowl as if you were just barely flushing. The flap and valve need checking.

Tightening a wiggly tank

The (usually 2 or 3) brass bolts extend down from inside the tank through rubber washers through the back of the seat and into metal or plastic nuts under the back of the seat. Tighten those bolts with a screwdriver from inside the tank and a wrench or pliers to hold the nut still.

If the rubber washers inside the tank are gross and slimy, or if they are visibly crumbling, they need to be replaced.

**Replacing the tank bolts and/or washers **

Turn off the water at the wall and hold down the flush handle or prop open the flap inside the tank. You'll need a rag or sponge to remove the puddle of the water at the bottom of the tank. Undo the bolts from inside the tank by following the instructions under tightening a wiggly tank. If you are replacing the washers, any home improvement store will sell assorted black rubber washers in a little pack for maybe $2.

Checking/replacing the tank seal

If the water is coming from between the seat and tank but the tank isn't wiggly, you may have a crumbling seal. Some, but not all, toilets have a rubber seal like a big o-ring between the tank and the seat around the big hole where water flushes into the seat from the tank. Remove the bolts following the steps in tightening a wiggly tank and carefully lift the tank off of the seat. (Careful to avoid dropping it on the floor, toilet, or your feet!) Turn the tank upside down. If there is a rubber seal around the big hole, take it to the hardware store and ask for help finding a replacement. There may not be one for your specific toilet, in which case you'll need to check Amazon or the toilet manufacturer (Kohler, American Standard, etc).

Checking the flap and valve

The flap is the flattish lump of rubber in the bottom in the center of the tank under the water. To check if the flap is leaking, watch the leak in the bowl and stick your hand into the tank to press down on the flap. If the leak stops, you might have a bad flap. If the flap is gross and slimy, the rubber has gone off and you have a bad flap.

To see if the valve is bad, watch the leak and pull up on whatever kind of float your toilet uses. It could be a rubber balloon on a horizontal stick, or a plastic cylinder that slides up and down a pipe. If forcing the valve closed stops the leak. You need to adjust or replace the valve.

Replacing the flap

This is easy. The flap clips on with usually two little plastic hooks, and you should be able to gently pull it off. Disconnect the chain that goes up to the flush handle or float ball or whatever. (It varies) Replacement flaps are $10 and come in brand-specific and universal types. They're pretty much universal anyway.

Adjusting the valve

Unfortunately this varies a good bit depending on the valve you have. If you have a balloon on a stick, you can bend the stick upwards slightly or unscrew the balloon slightly to move it farther out on the stick.

If you have the weird plastic pipe and cylinder arrangement, there's probably a plastic screw on top that needs turning.

Replacing a valve

Turn off the water at the wall. Drain the tank. Disconnect the water supply hose from under the tank - it'll dribble so be ready with a rag.

There is another nut around the same threaded pipe that the water was connected to sticking out of the bottom of the tank. Unscrew this nut. The valve should just lift out now.

The toilet lid is purely cosmetic, it has nothing to do with a leak

Were you standing on it hanging a clock perchance?