Spring is a point where groundwater flows out of the ground and is thus where the aquifer surface meets the ground surface. It is dependent upon the constancy of the water source a spring may be ephemeral or perennial. The water issuing from an artesian spring rises to a higher elevation than the top of the confined aquifer from which it issues. When water issues from the ground, it may form into a pool or flow downhill, in surface streams. The minerals become dissolved in the water as it moves through the underground rocks. This may give the water flavour and even carbon dioxide bubbles, depending upon the nature of the geology through which it passes. This is why spring water is often bottled and sold as mineral water, although the term is often the subject of deceptive advertising.