Basically, the Water Jet is when a girl fills her mouth with hot water and gives her man a blowjob. While blowing, she garlges and swishes the water around in her mouth, giving the effect of a water jet in a hot tub. This move was first described by the Red Hot Chili Peppers frontman Anthony Keidas in his autobiography "Scar Tissue", but was never given a proper name. So for lack of a better name, Water Jet it is.
Dude, my girlfriend just gave me a water jet last night. She blew so hard it felt like I was pressing my dick against a real water jet. I bet if you ask nicely, I bet your girl will give you one too.