Water stored in above ground tanks in below freezing temperatures is susceptible to freezing. Methods to prevent water in above ground tanks from freezing can include, recirculating the water in your tank, insulating your tank, building an insulated enclosure around your tank, or heating the water inside your tank. Water stored in underground tanks is less likely to freeze. In order to prevent water stored in underground tanks from freezing, the tank should always be buried at a depth that is below the frost line in your region.