Fuhhh. before this I have never heard of such thing. What's worst I never heard of a cistern before. In BM however, I know what that is. LOL but not as in ancient or old underground cistern k. Silly me for not adding my general knowledge. So lot of thanks to the Inferno book, my on and off diligence trait and mostly thanks to my curiosity trait. HA HA! Okay, cistern, based on wikipedia : A cistern (Middle English cisterne, from Latin cisterna, from cista, "box", from Greek κίστη kistê, "basket") is a waterproof receptacle for holding liquids, usually water. Cisterns are often built to catch and store rainwater. Cisterns are distinguished from wells by their waterproof linings. However, , if you have slight doubt on wikipedia, there's always other option. www.merriam-webster.com/dictionary/ cistern an underground container that is used for collecting and storing rainwater. I'll also give you the DBP's definition of cistern in BM