DIAGNOSIS A small amount of moisture or condensation around the rim as it heats is normal, but a steady drip or stream of water from under the lid means the seal is compromised. The gasket might be dirty, dry, or not seated properly.
FIX 1) Let the canner cool and depressurize completely. 2) Open it and remove the lid gasket. Inspect it for cracks, nicks, or permanent folds. 3) Clean the gasket and the channel it sits in thoroughly. Dry both completely. 4) Apply a very light coating of vegetable oil or glycerin to the entire gasket—this is key for the Presto rubber gaskets. It keeps them pliable and helps them seal. 5) Reinstall the gasket carefully, making sure it's not twisted or pinched anywhere in its channel.
IF THAT DIDN'T WORK Check for damage to the sealing surfaces. Run your finger around the polished rim of the pot and the matching surface on the lid. Feel for any dents, deep scratches, or warping. Even a small imperfection can prevent a seal.
HEADS UP If water is leaking, steam is also leaking, and you won't be able to build or maintain pressure. Don't proceed with canning until this is fixed. A leaking canner will not process food safely. If the gasket is old, hardened, or damaged, replace it—they are a consumable part.