Water exhibits surface tension. Surface tension of water or the ability of a substance to stick to itself makes water an excellent substance to float heavy objects on its surface. The molecules of water on the surface of a calm and quiet pond tend to be drawn into the liquid, so that the liquid surface is taut, like a sheet of rubber drawn over the open mouth of a jar. This tautness is caused by surface tension.

Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer. The surface of water can support small objects like a sewing needle until the surface tension is broken. This "skin" on the water aids the growth of mayflies and caddisflies that are attached to the water’s surface. However, surface tension can also trap flying insects that accidently fall into the water and are unable to fly out.