If you slow the motion of water molecules down, what are they more likely to become?
If the kinetic energy of water particles were to slow down, that means the temperature of the particles are dropping.
As a result, it will form ice.
Kinetic energy and temperature are directly proportional. If heat is added, the kinetic energy increases, which forms a gas (if original state was liquid).
Vice versa and you get ice. This can be accomplished by freezing the water.
Hope this helps :)