So presumably when you see pictures of kids in the spray from hydrants on hot summer days they are accessing wet wells?
No depends on the freeze zone of the area they are located in! A wet well will freeze and bust in the winter. All pipe lines are engineered accordingly! Water is just supplied in a different manor. A wet well has water it it all the time and a dry well drains and is dry when you shut it off. Some areas of the country the freeze zone can be as much as 9 ft deep.
LA never freezes normally so wet wells are utilized.! What you do not see there is a pipe 6” in diameter that feeds that hydrant @ normally 160 psi. To get a spray from a hydrant it is just cracked open a bit. Otherwise it would flood the street.