Water-based varnishes are called that because their solvent is water-based, instead of being oil or alcohol-based like more traditional varnishes. The solvent is used only to dilute the varnish to keep it in a liquid state during application. The goal of varnish is to harden once applied to the floor. The process that causes it to harden is the evaporation of the solvent. In this case, the water evaporates from the surface of the floor to dry and harden the product, allowing the resin to act.