New HK $10 Notes

Yes, they are waterproof and won't be easily damaged even if you put it into water. Have a look at this newspaper article:
http://hk.news.yahoo.com/070709/12/2b3ym.html
The reporter put a new $10 note in the pocket of a jacket, washed them in a washing machine & did not see any apparent change afterwards (except getting wet).
You can swim with them in your pocket if you wish.

yes it is waterproof, you can go swimming with them in your pocket