I think that, in our culture, showering is a pretty private activity. It's a bathroom activity - and most of those you do alone, even if some of them (brushing your teeth) are less potentially embarrassing than others (sitting on the toilet). Plus, you're naked in the shower, and modesty dictates that noone is allowed to see your naked parts, but for a few exceptions (close relatives when you're small, friends when you're drunk and goofing off, spouses when you're horny). If that's not enough, you're rubbing your hands all over your naked, wet body in the shower, and hell if that's not at least a little bit sensual (even if you're not thinking about that when you do it).
Most people shower alone, and have an expectation of privacy when they're showering - again, but for a few exceptions, like if you're showering with an intimate partner, or if you're a kid in the bath with your siblings. Of course, not everyone goes by those rules. Nudists, for example, are by definition lax about modesty regarding nudity, and in many nudist resorts and locales, there are outdoor shower facilities (like the indoor kind you find in locker rooms, that go largely underused thanks to a combination of excessive modesty and homophobia, due to locker rooms being unnecessarily segregated by gender) where men and women old and young alike all shower together without a care in the world (then again, they're hanging out naked together without a care in the world in the first place).
You, of course, don't shower with strangers in these places, as that would be pretty awkward, but you could very well find yourself showering next to, or in front of, complete strangers as well as friends and family members. And really, once you get over the thought that "this is supposed to be a private activity", it's really not a big deal. We all shower. And nobody is particularly interested in your shower routine - you do what works for you. Unless they're a jerk, nobody is going to criticize your routine or anything of the sort.
But what of the sensual element I mentioned above? Watching an attractive person shower can be a highly sensual experience, I won't deny that. In nudist contexts, this sort of thing is strictly verboten, because it is impolite, and people don't go to nudist resorts to be gawked and leered at. And what's more, if you aren't intending to be watched, then having someone's eye on you can make you incredibly self-conscious. But in a more appropriate context, it could be a very sensual experience, both for the exhibitionist in the shower, and the voyeur watching.
Now I get the sense that some people would think, "who would want to watch me showering?" And if they're not particularly attractive, then maybe the answer to that question is, not very many people. But if they are, or if they are more attractive than they think they are, then there might be some people out there who would be interested. Now, how is one supposed to feel about that? Cultural values regarding modesty dictate that we ought to feel a bit creeped out that somebody would derive pleasure from looking at us naked. But I say, why the hell should that bother us? It's only natural.
I guess if you think about it reflexively, if it were you looking at yourself, you'd probably be a bit creeped out, because I imagine that most people are not particularly attracted to themselves (I may be a bit of an outlier in that sample). But think about somebody else, who is very attractive to you. Of course, if you've internalized the sexual shame that society has pounded into your brain, then you'll probably feel bad about "lusting" after another person. But if you're comfortable with your perfectly natural and healthy sexual feelings, then you might recognize that getting to watch an attractive woman (or whoever you might be attracted to) taking a shower (preferably with her permission, firstly because it's more fun if the other person is enjoying it too - although your feelings on that may vary - and secondly because it's more ethical that way, which entails less guilt) is a pretty exciting thing to do.
Now, just conceptualize it this way. There might be some people out there who are attracted to you, and would enjoy watching you take a shower. It's not creepy or anything, it's just natural sexual curiosity. And there are probably a lot of other people who have absolutely no interest in watching you take a shower (and not necessarily because you're ugly, they may just not be attracted to men, or whatever the case may be). There's no reason to feel dirty about letting the people who want to see it see it. And if some people don't want to see it, that's perfectly fine - and they really should not criticize you for letting others who do want to see it see it. That's called censorship - keeping something from someone who wants to see it. If somebody thinks you shouldn't give a naked picture of yourself (just as an easy example) to a person who wants to see it just because the first person (who wasn't asked and shouldn't be butting in) has no interest in seeing that sort of thing, they are forcing their interests and morals on you, and attempting to restrict your freedom of self-expression. Don't let them do that to you. Don't let them make you feel guilty or dirty for engaging in this kind of activity, either.
On a related issue, I hold firmly to the belief that letting a person see you naked, or even going so far as to let a person watch you masturbate, is not equivalent to giving them permission to have sex with you. This is why you should not feel awkward allowing people you are not attracted to, to be turned on by you. You can give people the gift of sexual excitement, without committing to engaging in any kind of sexual contact with them (that's the beauty of voyeurism/exhibitionism). To use a more concrete example, say you're a straight man. If a gay guy hits on you, you have no reason to feel intimidated, because simply being attractive to a gay guy doesn't make you gay. Attraction, as you probably know, is not always a two-way street. It doesn't have to always be a two-way street to be worth anything. If you're willing to give your attractiveness out without reciprocation, and if others are willing to be attracted to you without expectation of reciprocation, then more people can be happier and hornier and more relaxed about their sexuality without a need to put pressure on those they are attracted to who aren't attracted back.