Also, anyone who's worried that it is urine should go to the loo before sex, once you manage to squirt you'll see that the fluid's different. It tastes different, smells different, and has a different consistency.
Once you get the hang of it you'll probably be able to control when you do it, handy in situations where a lot of liquid would be too messy/inconvenient, or when someone's asking you to squirt all over them.
Also - invest in some of those waterproof-backed picnic blankets, or you might end up with a lot of washing to do! :D