The town built a big building by the river where it cleans its used water. The town calls it the water-cleaning center.

The water-cleaning center, step by step: screens, settling tanks, tiny living things, a test.

First, screens catch the sticks and paper. Then the water stands still in wide tanks, and the mud sinks to the bottom.

The town calls these wide tanks the settling tanks.

The settling tanks. The water stands still, and the mud sinks.

Next, tiny living things, far too small to see, eat the waste that is left in the water.

Last, the town tests the water.

Is the river below the town clean now?

Yes, it is. The clean water goes back into the river, and the river below the town stays clear.

The same town, two ways: the used water sent straight back, or cleaned first.