Because of this, delineating recharge areas can become quite complex since the water may not take the same route twice. The amount of time it takes for water to pass from the surface and out the spring affects many qualities of that water. Particles remain in suspension, resulting in muddy or greenish colored water, which is not that different from surface water. It is during such flows that one may observe the true vulnerability of karst, since relatively large objects can be emitted from the springs under high velocity conditions. If water is underground for longer periods, a crude sort of filtering occurs.
Particles drop out of suspension, as do such things as twigs, leaves, etc.
The content of living organisms in the water shifts, as those which require light to survive die off, and others which do not, flourish. The water becomes clear. The process is very similar to primitive primary water treatment through settling and aeration. Just as in a water treatment plant, the water is affected by the materials it passes through. Unlike the human system, though, these materials are not controlled, but determined largely by chance.