I'm about to use the locker room shower and I'm going to take 10 minutes.
Is there a reason you're going to take 10 minutes?
I like to take my time in the shower.
Showers are really nice, but this is a public place so it's better to be considerate of other people's time. There may be lots of other people waiting to use the shower, so try to keep it short and enjoy longer ones at your home.
It's water. Who cares?
Not only is water a natural resource that shouldn't be wasted, but you're taking up a shower that someone else is probably waiting to use. If you want to take longer than normal showers then the appropriate place to do so is in the privacy of your own home.