The opening of a new water park in Orange County has some residents excited, though others are wondering how much water the park will use amid a prolonged drought in Southern California. The giant wave pool, lazy river and slides at the new Wild Rivers in Irvine will be filled with thousands of gallons of water in the coming days.  …  Experts said it will initially take up to 900,000 gallons of water to get the water park up and running.