How do hard water and soft water differ?

How does water-based water-repellent paint work? Did a burger on top of my normally vegetarian diet cause my belly ache? Why has no one invented a silent vacuum cleaner? And if an egg yolk ruptures, does that mean the egg is bad? Also, why the obsession with electric cars: surely hydrogen is the future? How do hard and soft water differ? And can blue-eyed parents have a brown-eyed baby? Join Dr Chris and Kieno Kammies for the answers on this week's Ask! The Naked Scientists...