How to bring booze into a music festival

A plan to smuggle in some booze into the venue from a guy in my lab who did it last year, successfully. Here it is: Before leaving, go to a U-brew store and buy some self-sealing bottle caps. When you cross the border, buy a bottle of clear booze (e. g. vodka, white rum). Also buy a flat of small water bottles. Put your booze into the water bottles and screw on the self-sealing caps. Voila! Now you can put your booze in with your water and bring it in to the show without any hassle. The only draw-back is that you have to buy mix or drink warm straight booze...