Cohesion is a property that makes molecules stick to themselves. Water has high cohesion because it's very polar and forms hydrogen bonds. In other word, it's attracted to itself. This creates high surface tension. Here are some effects that result:
1. Water forms spherical droplets and "beads up" on surfaces
2. Water will "mound up" over the top of a glass when over-filled
3. Water-skipper bugs can walk on top of water
4. The surface of water has resistance, as felt when doing a belly-flop
5. Water has a higher boiling point than similar compounds such as H2S.
6. Water has low vapor pressure. It doesn't evaporate as quickly as similar liquids.
7. Capillary action - water moves up tubes of thin diameter. This helps transport substances in plants.
Water's hydrogen bonds create another interesting property - the density anomaly. Unlike most substances, water expands when it freezes.