CardHolder for sport Bottles

When I go to my local gym, than I need a towel, my membercard and a waterbottle.

I need my the Membercard to close and open my wardrobe. But at my fitness time, I don't know, where I keep this single tiny card.

Sometimes I found a other Membercard in the gym, so that I think, I am not alone with my problem :D

So I designed a holder for standart cards, where I can wear my card with my waterbottle.

I designed for standart water bottles for cycling. This bottles have a typical recess f