Why does my dog do these things?

I have three water bowls tastefully strewn about the house so Blondie never has to go but a few steps to get a drink. And even if they were for some reason empty, experience has unfortunately shown me that she will happily dip her head in the toilet bowl and drink as though it were the nectar of the gods. So why… WHY… does she go out for her walk with me and stop at every dirty puddle with a greasy film and god knows what at the bottom and lap it up as though she’d been in the Sahara for a year with no liquid refreshment at all? Even more puzzling, why does this never make her sick? I worry about her food bowl being clean and she’s drinking water that would kill most people without showing the slightest ill effects.

Is this why they call it a dog’s life?