# Why ground water is cold during summer and hot during winter?

I've heard somewhere that during summer the temperature of ground water is lower than that on the Earth while during winter the temperature of ground water is higher. How is this possible ?

• I always thought the answer must contain the $4^{\circ}$C density anomaly. If water would become denser the colder it gets, wouldn't the warmest water always migrate to the top to minimize buoyancy forces? Aug 1 '21 at 12:56