I have found that my cup takes on sea water when I dive and surf. It won't be full but I will get leakage of watered down blood, and when I empty my cup it is half full of blood and seawater mixed together. It never leaks when I am not in the water.
It may be relevant that I have a low cervix and short vaginal canal - my small ladycups have their stems cut off and they couldn't fit inside if they were any longer. My cervix sits in the cup. My cups have never created a "suction" seal, although they do seal. And, maybe relevant, I also always had the bottoms of tampons take on water when swimming/diving.
I'd like to hear from those of you who have had the same thing happen (cup leaking and taking on water when swimming). And to know:
(1) if you have a low cervix / short vaginal canal,
(2) if your cup creates a suction type seal,
(3) if you have had any luck switching to a firmer or softer cup. (i'm thinking of next trying a soft small sckoon)
(4) anything else you think is relevant
These are 3 things that i thought might be contributing to this happening.