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 shall observe that :

At $4^{0}C$density of water is maximum .so if water is heated and cooled above and below $4^{0}C$then its density will decrease,so the volume will increase,hence water overflow in both if the beaker is filled up to its brim .