Underground fiberglass potable water tanks conform to NSF 61 standards, and offer a standard 30 year warranty. Underground fiberglass tanks are equipped with an integral resin interior, with a polyester resin & glass exterior, eliminating interior and exterior coatings. Underground fiberglass potable water tanks are lightweight, yet strong due to the proprietary rib structure. Choosing an underground fiberglass tank will eliminate freezing, space usage, aesthetic eyesore, vandalism and seismic precautions.