give you the answer.   Squirting that is real comes from natural lubricant created in the Skene's gland.  As some women get more aroused,  the opening sometimes swells shut, trapping the fluid inside.  It builds up and when she O's, its involuntarily released and squirts out in a single gush.  If its more than two or three tablespoons of fluid, then it probably is urine.  Many women lose bladder control start peeing when they O.  Its usually a half a cup or more, which is way more fluid than an engorged Skene's gland can hold.  

 
There was a girl in SoCal that was famous for squirting, but it was a trick.  She would insert a little syringe bulb full of water inside of her pussy, and would squeeze her kegels to squirt it out to coincide with a fake orgasm.  She managed to fool about 90% of her customers.