There used to be a old Yahoo group dedicated to this very thing. I just checked and I can't find it anymore....so I guess that really wasn't helpful at all. :(

Thanks for looking and keep trying please :)

I don't know if it's ok to post this here... but this link will take you to a place where you can get thread that vanishes after it gets wet.

I remember that yahoo group. It's been gone for sometime now...

http://www.sewthankful.com/SuperiorVanishThread.html

Thanks for that, so with the right thread modifications to a strappy dress or skirt and the accidental spilling of drink while out one night, this could have a great effect, anybody tried this? :)

This would be especially beneficial on a swimsuit or bikini.

Found it in UK
 

Found this thread now in the uk, soluble thread, will order as swimming is a hoby and I could modify swim suit, also have very flowing strappy dress to midify quite low at back so she does not wear with a bra, this would be the one for a night out spilage of water on back, also halter neck could have same effect, would have cam ready for that to.
Any other ideas though that would have a timed effect for zip stitching etc (im not good at sowing!) this way I can apply before we go out and then wait as the night goes on, there must be a chemical expert out there somewhere! :D

Not an expert...just a fellow perv, but what about using rice paper rolled together to make a strap...should dissolve nicely.