Why the ground water is hot in winter and cold in summer?

The water itself isn’t any hotter or colder, it’s exactly the same temperature. It just feels hotter or colder because air is cooler or warmer.
The ground has a very stable temperature, and more than a few feet under in most places and the temperature varies by just a couple of degrees all year round. That’s; why wine and vegetables are commonly store din cellars, to protect them from the heat and cold. Water in the ground has an equally stable temperature.

So in summer the water is going to be several degree cooler than the air, and so it will feel cold. In winter despite being the same actual temperature it will be several degrees warmer than the air, and will fel warm.

it's relative to you! it's because water doesn't change temps like your body does, so it seems warmer in the winter (When you're cold), and you're hotter in the summer, then water is!

It is relatively hotter in winter and vice versa. It is because water has a higher heat capacity. Heat capacity is the energy needed to change for 1 degree change in temperature.
So water takes longer to heat up and longer to cool down, so relatively it is hotter in winter and vice versa.

That they are good for health, however if you are asking which is better for diet in cases like this all vegetables would do well