A water tank is a large container that stores water for a variety of uses, including:drinking water, irrigation, fire suppression, farming, chemical manufacturing, and food preparation. Water tanks can be atmospheric or pressurized. Atmospheric tanks are more common for outdoor, large-scale use, while pressurized tanks are used for indoor applications. Water tanks can help save on water bills, as the collected water can be used for many things, such as: Watering gardens and lawns, Flushing toilets, Washing clothes, and Washing cars.