No, girls don't seem to get the pat-down search, although I wouldn't assume this.
As for the searches themselves, people seem to get random searches, but they aren't that thorough. I mean water is something you can afford to lose anyway, so it's no real disaster if they find it.
They seem to be concentrating far more on cameras over there, so if you take a bag, expect them to look inside.
It's a shame really, as the prevalence of E sellers in some clubs is over the top, and there is little to prevent someone bringing a weapon in with them.