A beaker is filled with water at 4°C at one time; the temperature is increased by a few °C above 4°C and at another time it is decreased by few °C below 4°C. One shallobserve that :

At 40Cdensity of water is maximum .so if water is heated and cooled above and below 40Cthen its density will decrease,so the volume will increase,hence water overflow in both if the beaker is filled up to its brim .