Why are humans so inefficient with water?

During the course of human evolution, water has been plentiful and available enough that humans haven't needed to be as efficient with water as some other mammals. This includes water in foods, such as fruits. Sweating is a human adaptation that aids in thermoregulation, which uses water but allows humans to be more active in warmer environments, so they were able to expand their home range. When water consumption is limited, the kidneys respond by producing more concentrated urine, thus conserving some water.