The water storage capacity of a built object is the total amount of room available for storage of water in reservoirs, tanks, containers, or other storage facilities within the structure or object, expressed in cubic units of volume. This does not include space within pipes, drainage systems, gutters, sinks, tubs, or other areas where water is used or transmitted - it only applies to storage areas. In a water tower, water tank, or other object devoted expressly to water storage the value of this field is usually equal to the value of its overall storage capacity.

This measures room for contents and not enclosed building space. A warehouse has a storage volume smaller than its architectural volume, because aisles, offices and the space above the racking are not storage.

The figure belongs to the installation rather than the building. Replacing racking or tanks changes it while the structure stays as it was.