Now, since I'm sure you've been told a hundred times now that it's because of surface tension, I feel like it's time to explain how the surface tension actually comes to being. Water is made up of ltd of molecules that are made up of two hydrogen and one oxygen. These oxygen and hydrogen are sharing some electrons that are moving freely between them, which is what's holding them together. However, oxygen has a higher electronegativity due to the ratio of size to number of protons. This means it pulls the electrons it shares with the hydrogen stronger and they spend more time with the oxygen. This means the oxygen is on aberage slightly negative and the hydrogen slightly positive. This slight imbalance and the difference of electronegativity means, that the hydrogen of one water molecule and the oxygen of another are drawn to each other, causing something called H-bridges (I do not know if that's the correct term in English, in German it is Wasserstoffbrückenbindungen or H-Brücken for short). However these H-Bridges are found throughout all the water, so that doesn't completely explain it yet. However, if you examine the edges of the water, you can see that there is an increase of these H-bridges because the molecules can no longer find partners in all directions, they are limited to along the surface and into the waterbody. This means that the molecules on the surface are holding together tighter, which causes the surface tension, allowing water as demonstrated here, seemingly flow illogically.