I am 99.9% sure that it won't work under water because of the transmission protocols...they are coming out with Pod (for less $$) that will solve this issue...you are in same boat as me. So, I would wear the Polar HR during the swim, bike, and run, but have the small pod taped under the seat that would convert my quarq to BLTE for the v800...This is due out any day and the day it is, I will provide a definitive answer...
http://4iiii.com/products-pods/
http://4iiii.com/products-pods/