During a summer with little rainfall, your house on a hill slope experiences an interval during which your well runs dry. You have to borrow water from your neighbor who lives downslope from you. Why does your neighbor have water when you don’t?
You don't have water because of two possible reasons:
Because of the summer and the little rain, the underwater supply goes low.
The slope in the hill you live makes the underground water goes down by the effect of gravity. Imagine the underground water like a small tank, when the water is reduced for any reason the bottom of the tank will have the remaining water, while the top part will be "empty".
