What water tank is best for you? Which is better and which will last longer? When choosing a water tank to keep water, there are two most common choices: the poly water tanks and the galvanized steel tanks. The most widely used in many areas are the poly tanks because of its adaptability and durability. They can be used no matter what temperature of the weather you have in your location. Since they are light in weight, they can also be used above and below the ground as they can easily be delivered and installed in a desired place. That’s all.