I'm surprised to hear that your wafer came off after just one bath. Had you already had it on for several days? I get mine very wet in baths, showers, even swimming sometimes, and it always stays put. You could try a different brand, but I could also see not wanting to change your set up.
Something I use when I know I'll be extra active, or doing something that makes me want to be sure my wafer is VERY secure, is the Sure Seal Rings. They work GREAT and are super comfortable. You can go to the website and request a sample.
www.alpglobal.com/Sure-Seal-TM-Rings.html