Panties used during the shoot

I am curious to know, you use so many pairs of panties during your shoots. Do you supply the panties that the models pee in or do they sometimes use their own panties to pee in? I am sure you have a very big account at a female underwear store if you purchase all these panties yourself. Just curious to know how it works.
That would be interesting to know.....maybe a combination of Both. I've bought some girls panties before so they could pee in them for me.
You shouldn't need so many - they can always be re-used.
No need to even wash and dry them between photoshoots.
For some reason I find it very sexy thinking that a girl pulls a pair of panties on that another girl peed in and left to dry.
Have this ever happened in the panty wetting landscape that anyone knows of?