Let's recall a little fluid mechanics. Molecules are capable of exerting electrostatic forces on each other. In the case of like molecules these are called cohesive forces. For example water molecules exert cohesive forces on neighboring water molecules. Meanwhile unlike molecules (for example water molecules and playing card molecules) exert adhesive forces. In the video it appears that both adhesion and cohesion are in play. The adhesion between the water and the card (and the water and the glass) keeps everything "glued" together while the cohesion between water molecules prevents the water from "breaking" even when some fluid starts to leak out of the bottom of the glass. What's surprising is how strong these forces can be. I tried this trick using a completely full 550 milliliter bottle of water. That's around 1.2 pounds of water. The card held. However, make sure you use a glass with a relatively wide and flat rim or the forces won't be sufficient to impress your friends, neighbors and potential dates.