What do you think is the most important invention in history?

I think the most important invention in history would have to be the sewage system/water treatment plant. Everyone has to use the bathroom, wash dishes, take a shower etc....that is why these systems are vital, especially in our modern-day living. Just think what it would be like today if sewage systems were not around...we would still have to use an outhouse!!! Or worse, we might just have raw sewage lying around in city streets (in some ancient civilizations that's what happened--the people living in a city would just dump their sewage onto the streets).Yuck. Also, look at Africa and other prevalently underdeveloped places--they don't have sewage systems, and as a result, they usually have raw sewage contaminating their fresh water. This then leads to disease and lack of water resources which in turn causes dehydration...definitely not good. And on top of that, the people living in these places can't even really take a decent bath!  Just think how fortunate we are to simply be able to turn on a faucet and have crystal clear water come out. I don't know about you, but it never ceases to amaze me! I am so thankful that I live in America where raw sewage is not floating about in all the available water sources around! And I am glad that sewage systems/water treatment systems are in effect all over this country and many other countries. These systems are ever so important!!!