Groundwater meets the surface in a stream, as shown above, or a spring (figure 1). A spring may be constant, or may only flow at certain times of year.
Figure 1. (a) Big Spring in Missouri lets out 12,000 liters of water per second. (b) Other springs are just tiny outlets like this one.
Towns in many locations depend on water from springs. Springs can be an extremely important source of water in locations where surface water is scarce (figure 2).
Figure 2. In the dry Arizona desert, Oak Creek and many other streams are spring fed.