I don't mind getting wet : )
Speaking for myself it's something I would prefer to know before our time together. I'm sure most ladies as myself take time preparing ourselves before time with a gentleman. Certain things I would change in that preparation if I plan on getting wet. Like waterproof mascara : )

In my limited experience, and in reading some of the reviews, it seems that a good number of the well reviewed ladies on this board join you in the shower at the beginning of your time together. Keep digging, I'm sure you'll come across some ladies who would be happy to join you.

I have taken showers with some of my 'friends'.  I prefer knowing ahead of time because you are right.  If I take the time to do my hair and makeup just right, getting in the shower is not something I want to do.

I usually mention that I would like to take a shower and freshen up when I arrive. If I've already met the lady, I mention in the last email she gets from me just prior to the date that she is welcome to join me if she'd like. That then gives her the choice of joining if she desires.

One of the hottest emails I got was from a lady I had seen before who I had only said in an email I would need to shower first. Unprompted, she was the one that replied back to me asking if she could join me. That raised the anticipated eroticism level!

I understand that some ladies can't due to hair/etc., but it is always a nice moment if they can share a bit of 'water' time. Rubbing soapy bodies together is a delightful sensation.

I think you are more likely to get a positive response to it on extended dates/overnights.

Re: How to ask?

Me personally, I just tie my hair up and try not to get my face wet...Still can enjoy a shower. It's fun!!!