system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How does a well work? Is there a finite amount of water in a drinking well? Why is it okay to drink? Do they somehow replenish water or if they dry up that is it?
gpt
Wells work using the water underground. The ground is full of little cracks and lets water seep down into it when it rains. Some of this is lost on the surface due to evaporation but some of stays in the ground.  Using scientific methods we can see how far below the ground the water is. This is known as the water table. If you dig a hole that goes deeper than the water table, the water, following gravity, will flow into the gap you have just dug. This fills it up the hole and is how wells replenish thier water. 

The best example i can give of this is digging holes in the sand at the beach. The water table there is pretty much level with the sea. When you start digging the sand is dry, then it seems to get more 'wet' the deeper you go. And when you get below the water level the hole fills with water quickly.