Narrower tube openings allow capillary action to pull water higher.
Capillary Action .....in Action!
Capillary action occurs because water is sticky, thanks to the forces of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances). Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The height to which capillary action will take water in a uniform circular tube is limited by surface tension and, of course, gravity.
Credit: Dr. Keith Hayward