Don't throw the baby out with the bathwater

I think that proverb is a warning against discarding something valuable or important while disposing of something worthless, but it seems to have a literal origin. During the Middle Age, most people bathed once a year. Even when they did bathe, the entire family often used the same tubful of water. The breadwinner of the house bathed first, followed by other young males, then females, and finally the babies. We can imagine how thick and cloudy the water became by that time, so the infants' mothers had to take care not to throw them out with the bathwater when they emptied the tub.