Depends on the vehicle, engine temp, and a few other factors, but yes theres a chance it will. If the car happens to run the vac/pressure test as you open the tank, then it will, but i would say, maybe 10% chance.

Water is heavier than brake fluid, unless you have clear calipers you will never know whats in the bottom of the calipers at the lowest point. Ask me how many 10+ year ild toyota 4 piston calipers i have changed that the lower piston or both are seized because " toyotas only need oil changes"