Answer:
At atmospheric conditions, the water will freeze when its temperature is reduced to saturation temperature. When the temperature is decreased, the molecular activity/kinetic energy of the molecules will also decrease resulting more intermolecular force attracting between the molecules. Once the inter molecular forces increases that much that it does not allow any mobility with in the molecules (though the molecules will vibrate in that stage too), then the substance will change its phase and it becomes a solid.
So Decreasing the kinetic energy increases the intermolecular attractive forces promoting the sudden change in phase causing the freezing of water at standard atmospheric conditions.