It is the location described by ancient sources, both Josephus and Pliny as where some Essenes resided. Archeology and pottery shards corroborate this as an Essene settlement. However, there are many who still debate this.
Water, it all boils down to water. Water dominates where settlements can be on the west bank of the Dead Sea (in Roman Times it is called the Asphalt Sea).
Ein Gedi has a spring, Ein Feshka has a spring, in fact the word “Ein” means spring. But Qumran has no spring, but it is near a wadi, or dry stream that will flow during heavy winter rains. There is a series of aqueducts that divert some water into cisterns for storage. The size of the water reserves gives an estimate of the population that could live there. Only a dedicated or desperate group would live in a location without a reliable source of water. But then again, 2,000 years ago, there may have been a different rainfall pattern.