A water tower is a freestanding tank constructed for holding water, which is elevated off the ground for the purpose of increasing pressure within a water distribution system. The water tower may or may not be encased within a building-like structure. This category does not include water tanks on building roofs.

Elevation supplies pressure to the connected water system while the tank provides storage. An enclosing shell can hide the tank without changing that function.

The structure is freestanding. A water tank supported by an existing building roof has the explicit exclusion above, even when its elevation also assists water supply.