The Water Well is a Structure in the Primitive+-DLC of ARK: Survival Evolved. It is a storage device for containing water. The well can hold up to 200 water. It can be filled up by connecting it to irrigation pipes and it automatically fills up during rain or snowfall. Because of this, it is extremely useful when making new extremely inland bases, or bases up on mountainsides, as long as it is not undercover from the rain.
While you can fill the Water Well using a Waterskin, Water Jar or Canteen, you cannot directly refill a waterskin, water jar or canteen from the well. Connect a tap to a pipe that the water tank is connected to. The water will flow out of the tap to drink from or to fill waterskins or jars.
The Water Well's in-game description says it cannot be attached to Irrigation systems. This is mostly untrue - the Water Well can be attached to irrigation systems, but it cannot be refilled from them. The water only flows outward from the well.
The Water Well is treated as a thatch structure and can be damaged by anything except non-explosive ranged attacks.