Safeguarding against water penetration

When gluing a three-layered floorboard can I varnish the whole surface? I basically mean safeguarding against water getting into the crevices between the floorboards when mopping.

Do not clean floors with a mop. I warn you. Varnishing will not help because varnish is not water-tight and does not protect against moisture. In no event must water be left on the floor after cleaning. For protecting a floor I'd use anti-adhesive agents, which lower the surface tension of the varnish.