> Where does the water come from?

Uphill. Water soaks into the ground and flows within it, on top of the bedrock which is impermeable. When the terrain allows it can emerge from the surface lower down as a spring.

> Can it run out?

Yes, the same as any river if it doesn't rain enough uphill from the spring then it will run out.

> Can you increase the amount of water coming from them?

Not exactly? The water is flowing through the ground so you would need to affect a fairly large amount of ground to increase the flow rate.

> Springs seem to just be an infinite source of clean water

No, they aren't. Unless your mind is blown by rivers.

[removed]

This is a good question. Where does it "spring" from? I buy bottled water, or the refillable 5gl ones. So I understand that my water isn't fileted by a spring. But why does "Spring water" get a different designation than everything else? And does spring water get filtered, and if it gets filtered, but not distilled. Does it have parasites and shit? I'm not allowed to drink any water unless I boil, or something. Yet spring water is good for you...

> Uphill. Water soaks into the ground and flows within it, on top of the bedrock which is impermeable. When the terrain allows it can emerge from the surface lower down as a spring.

This is one means of creating a spring, but not the only one.

Another means is an artesian spring, where water pressure inside the rock can force water upward a short distance. The ultimate source of energy is still gravity (the source of the pressure is water higher up trying to force its way down), but the water doesn't flow exclusively downhill.

Rain falls and it becomes trapped between layers of rock in the ground resulting in an aquifer, pressure can build up forcing the water to the surface. https://youtu.be/xbUfVLxYVcE

Spring water is usually naturally filtered by passing through porous rocks on it's way out. In general it's gonna be cleaner than water from a river or a well, but of course not all springs are equal. Often you get delicious minerals dissolved in it which can be touted as "healthier" but mostly just taste different. Sometimes you get harmful compounds leeched into it. And the actual collection point usually isn't a rock, the water generally pools somewhere, it collects in a groundwater reservoir where bacteria can get into it.

So basically you still want to test a spring regularly to see if it's safe, and filter/boil it if you don't have the ability to test it.

But you know. If you are in a less developed place, and more or less already adapted to ordinary bacteria there, a spring in an elevated area that doesn't catch runoff is gonna be about the best source of water you are gonna get.