I learned that Birkei Yosef holds that non-mikvah water may be considered a chatzitzah. That is why we make sure our hands are completely dry before we wash them ritually. It may be why some are stringent to hold the handle of the cup with a towel. It may be why we wash a third time (instead of twice) i.e., before bread. It may also be why (just speculating) we are told to dip our hand in the mikvah water before holding a kli to toivel.
But a woman (and possibly also a man) can/always does immerse with wet hair. Why?
(I know she toivels more than once, so presumably one of the tevilot is kosher. But it seems she makes a bracha before even the first? Wouldn't that be a hefsek if the first dip is not a mitzvah immresion? Wouldn't it be ideal for her to dry her hair first [or else make the bracha after immersing]? Does anyone insist on this? )