What were the properties of water that allowed pennies to continue to be added to the glass of water?

The properties of water that allowed pennies to continue to be added to the glass are surface tension and cohesion. Surface tension creates a "skin" on the surface of the water, allowing the pennies to sit on top without sinking. Cohesion is the ability of water molecules to stick together, helping to support the weight of the pennies as they are added.