Water leaks into one lens, so you tighten the strap. It still leaks, but now the goggles hurt. A poor seal is not always a problem that more tension can solve.
Goggles need to suit the shape around your eyes and nose. The strap helps hold that fit; it should not be doing all the work of forcing an unsuitable frame against your face.
Check the seal before the strap
Speedo’s goggle-fitting guide suggests gently checking the cups against the eyes without the strap for a brief seal. Follow the product’s instructions and avoid pressing hard. This is a starting check, not a guarantee of comfort during every stroke.
Look at the nose bridge and the edges of the seals. Some models offer interchangeable bridges; others do not. A frame that pinches or leaves an obvious gap may simply be the wrong shape for you.
Adjust one component at a time
Fit the strap according to the manufacturer’s guidance and make small changes. Check that it lies as intended rather than twisting or pulling the frame unevenly. Hair or a cap edge caught under the seal can also affect the result.
Try the goggles in a safe, shallow or otherwise controlled pool setting where you can stop easily. Do not make an unfamiliar fit test the first task in deep or open water. Goggles are visibility equipment, not a safety substitute for swimming ability and supervision.
Notice when the leak occurs
Does water enter immediately, only when turning the head or after pushing off? Does the same side always fail? These observations make a conversation with a knowledgeable retailer or instructor more useful than “they leak sometimes.”
If you need to keep tightening through pain, stop and reassess the model or adjustment. Persistent eye discomfort, visual symptoms or irritation warrants appropriate professional advice rather than repeated experimentation in the pool.
Preserve the fit you found
Rinse and store the goggles as instructed, protect the seals from deformation and avoid rubbing lens coatings unless the maker permits it. Keep them out of a crushed corner of the swim bag.
A comfortable pair should let you pay attention to the water and your movement. The successful adjustment is usually the one you stop thinking about—not the one that leaves the deepest marks.