The surface tension in water makes it stick to the surface of objects. A classic situation is where the water runs under a soffit or under a stone or concrete windowsill, the water will run into the building along the horizontal surface. The situation is very easy to fix, all you need is a break in the horizontal surface. A vertical change in direction or a sawcut in the concrete or stone sill will cause the water to drip off the object. This is often referred to as a drip edge.