Short answer
A toilet leaking from the tank is usually leaking at the tank bolts, the rubber tank-to-bowl gasket, or the supply line connection, and sometimes through a hairline crack. Dry the tank, run your hand under each bolt and the fill-valve nut, and look for the first drip. Worn bolts and gaskets come as an inexpensive kit.
Updated 2026-10-09
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Find the drip
Dry the outside of the tank and the floor. Put dry paper towel under the tank and wait. Check, in order: the supply line nut under the left side, the two or three tank bolts underneath, and the joint between the tank and bowl.
Water beading on the whole tank surface on a humid day is condensation, not a leak.
Tank bolts and gasket
The rubber washers on the tank bolts and the big gasket between tank and bowl harden over time. Tightening a little can stop a drip, but over-tightening cracks porcelain. If it still drips, replace the bolts, washers and gasket together as a kit.
Supply line and fill valve nut
A drip at the supply connection is usually a worn line or a loose nut. Snug it by hand, then a quarter turn. If the line is old, replace it with a braided one.
If the tank is cracked
A hairline crack that weeps cannot be reliably repaired. Turn the water off and replace the tank or the whole toilet. A crack can split further without warning.
Common questions
Can I keep using a toilet that leaks from the tank?+
For a slow drip at a bolt, yes, for a short time with a towel underneath, but get it fixed soon. Water under the floor causes rot. For a cracked tank, turn the water off and don't use it.
Related
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