The ancients were very aware of subterranean water sources. For proof, you need look no further than the Old Testament's Ten Commandments, wherein the Israelites were forbidden to make graven images of any living thing, even from "...the waters under the earth...". Archaeological evidence from around the world demonstrates extensive ancient knowledge of well and canal systems which were sourced from underground aquifers. Field research has revealed that some of these systems were astonishingly sophisticated, employing basic hydraulic lifting systems, aqueducts, and other methodologies. There have long been traditional means of finding these underground water sources; for example, the presence of certain types of vegetation indicates the locations of aquifers; animals can be used to sense the presence of water; and primitive divining was practiced by tribal shamans. So YES, the ancients knew of, and used, underground water sources.