Why is crystalline aspirin washed with chilled water in the purification process? Take as example this 
or even better this:


  Wash the crystals with 2-3 ml of chilled water.


Why does the aspirin need to be cooled down? And why do we wash the aspirin with chilled water?
Because aspirin is less soluble in cold water. In fact, aspirin is not very soluble in water at all, which is why you are supposed to take it with lots of water. You are not "chilling the aspirin", you are preventing it from dissolving too much so that you have a better yield of your product. You wash it to remove impurities that do dissolve in water.