If Doggie would rather do -- well, anything, rather than getting into the shower, it's time for some changes. Forget dragging him into the shower and causing a mix of panic and chaos to ensue. The key is to make him believe walking into the shower is a lot of fun. Once the apprehension is over, Doggie might end up having a lot of fun in the water.
Forget water at first. You need to convince Puppy that there's nothing wrong with the bathroom and especially the shower area. So coax him into the shower area with treats. Ask him to sit down on the title and give him a small reward for obeying. After a few seconds, just step out of the bathroom and take him along with you. Repeat this several times over the course of days. This will get Doggie used to the shower area, so he doesn't associate it only with bath time.
Run the water near him once he's used to the dry shower. Don't get him wet. Just open the tap and let it run, so he gets used to the sound of water. If you have a detachable shower head, you can put it down on the floor and open the tap. The water will run and maybe touch his feet, getting him used to the idea that getting wet is OK.
Put a leash on before you walk into the bathroom. For the actual shower, you might need to hold Doggie in the area, so let him get used to the idea early on. You can let him drag the leash at first, but eventually grab it as he walks with you into the bathroom. Don't pull or make the experience traumatic. Just offer treats and rewards for following you into the shower.
Pick a quiet, relaxing time for the actual shower. After a long bout of exercise or during the hottest part of the day -- when Doggie is lazy and tired -- is best. Just call Doggie into the shower again or bring him in using the leash. Follow the same steps as you always do, but this time get the water on him, rather than just running. Keep the first shower short, unless Doggie is having a great time and can endure a longer bath.