How do we get waterways? How is it that water seems to collect in low places? From where does it come?

To explain very simply, we could start with evaporation of water from the seas, formation of clouds, winds to push the clouds over land masses, and the water to fall to earth in the forms of mist, rain, sleet, hail, and snow.

When it rains, we can see it soak into the soil, run off the streets into the gutters, and then, magically, into the sewers or whatever provisions cities make for rain run-off.
That doesn't help us with our problem, does it?

What happens to precipitation in mountainous areas? Most mountains are composed mainly of rock, which isn't very absorbent. What does the water do there? Let's make a mountain here in the classroom, and see what happens.

Place a large plate in a sink. Using plastic wrap and/or waxed paper, well crumpled, we will make a mountain on the plate. Tilt the plate, so the crumples are raised, like
mountains. The crumpled wrap represents a mountain range.

We will first put some crushed ice onto the mountain range, distributing it as evenly as possible (don't use much). This is "snow." Now, with a sprinkling can (the kind with small holes in the nozzle on the end of the spout) and very cold water, we'll pour a little "rain" in different places on the uphill end of the plastic wrap.

Observe what happens to the rain and snow. You will see that each trickle of water tends to collect and work its way downhill to the lowest point.

You will realize that, similarly, the water on mountains collects to form streams. The streams in turn collect, to form rivers that collect, to form bigger rivers and eventually
empty into oceans and seas.

What becomes of the snow and ice that stays in the high northern mountains and doesn't melt?