When people bring their dog in to me to get bathed, I've had a few warn me they really hate water... well, I find I have yet to find a dog that freaks out too badly about getting wet (the dryer and nails are the two things I find dogs are worst about, followed by long haired dogs + being brushed but only the long haired ones, and occasionally ear cleaning).
Now, I don't know if it is one of two things or if it is both:
1. They are in an unfamiliar environment and probably are nervous and maybe less likely to fight (long as you aren't doing something super horrible like trimming nails

).
2. We don't put them in a bathtub full of water. We use a device that they make a version for home use (I can't remember the name of it unfortunately). It basically is this sprayer that will spray water and with a click will also start spraying shampoo so you just spray them down to wash them. It may be easier to get them this way as you dont' have to show them a bath tub full of water and can tether them so they can't go anywhere (or wash them outside as the home version has a connection for both a hose or a shower head). Most even if htey freak at first give in within a few seconds and just let me wash them.