Recent studies have shown that people take time to pee in the shower. This is additional time that would not have been needed if one peed while putting shampoo in their hair or while they are using soap. They take time to aim in the gutter, while the water keeps running. While peeing in the shower, you flush as much water down the drain as when flushing a regular toilet. Therefore peeing in the shower doesn't save any water in most cases.
Peeing outside, however, does. This has been scientifically proven by Shullbit University.

No seriously, it's kinda true