Where did water come from, and why doesn't it go off?

Can sensors help keep our roads in good shape? If the Earth is round, why aren't the people at the bottom standing upside down? How efficient is the human body? Why can't periods be controlled like going to the bathroom? Do animals have periods too? Where did water come from in the first place, and why doesn't it go off? Dr Chris Smith and Relebogile Mabotja have the answers. Like this podcast? Please help us by supporting the Naked Scientists (thenakedscientists.com/donate)