4 layers with a 10-year guarantee for new tanks along with an invoice and warranty. Tank specifications: Copper outlets embedded in the tank, thermally insulated, with a manufacturing system based on casting rather than blow molding, and homogeneous layers that are well integrated. The tank is designed to store water in a clean and hygienic mold that prevents the growth of algae and fungi, with a mold that facilitates the cleaning of dust and sand accumulation.