Water repellent sealers form a hydrophobic barrier within the pores that causes water and other liquids to bead off the surface. By stopping the absorption of water on the surface, you prevent a variety of issues caused by water such as spalling, freeze-thaw damage, and salt damage.

This is what water should do to a properly sealed surface:

The best water repellent sealer to use is a high solids, solvent based silane siloxane water repellent sealer.