I remember learning in high school biology that whales have a really long loop of Henle. That's how they manage to drink salt water. If they didn't have that kind of renal physiology, they wouldn't be able to concentrate the salt enough to get useable water out of it.
It always made me wonder if engineers, or whoever comes up with these ideas could use whale anatomy to make more efficient desalination plants and help the world with an additional cheap and clean water supply.
@umbra21 - I believe kidney infections usually start out as bladder infections before spreading to the kidneys, so that might be why your sister gets that particular symptom first.