The thefts happened between last Tuesday night and Wednesday morning along Research Drive as well as West Lugonia, Almond and Bryn Mawr avenues. No arrests have been made.
It will cost about $40,000 to replace and repair the hydrants. In addition, public safety was put at risk because of the lack of water to fight fires.
Officials said thefts of hydrants, manhole covers and backflow devices have increased in several cities as the price of scrap metal continues to rise. Two bills that would make it easier to prosecute metal theft are awaiting signature from California Gov. Jerry Brown.
Anyone with information about the thefts was asked to call police at (909) 798-7681.