Water behaves very differently in the zero-gravity environment on board the International Space Station. Why do the water molecules in this floating bubble stick together? It happens because each individual H2O molecule is electically polarized, meaning the end with the two hydrogen atoms has a small positive electric charge, while the end with the oxygen atom has a small negative charge. Because of this, loose electrical connections called "hydrogen bonds" form between neighboring molecules: The positive end of one molecule hooks up with the negative end of its neighbor, and with enough of these hydrogen bonds in place throughout the bubble, the water clings to itself. On Earth, gravity overrides the effects of hydrogen bonds, making a bubble of water splat on the ground.