These vertical flat top tanks are freestanding with a flat bottom for indoor and outdoor applications. They also conform to the requirements of NSF/ANSI Standard 61. These tanks are manufactured from medium-or high-density polyethylene with UV inhibitors for longevity. The walls of these tanks are translucent for level viewing, and have gallon indicator marks so you don't risk running dry. | Ace Roto-Mold Vertical Flat Top Tank | Size 100 gal