The two main things a buyer should compare when choosing a water tank are its color and thickness. Plastic tanks also differ in shapes and sizes. The size of a tank depends on its purpose. Tanks for hot water are usually smaller, while tanks for storing rainwater may hold up to several thousand gallons. Buyers should choose water tank shapes based on the space they have available. For example, horizontal tanks are cheaper than vertical, but they require more space.
The most common problems with water tanks are algae growth and overheating of the tank that can damage it or lower the quality of water in the tank. If the color of the tank is light, it may let sunlight inside the tank, which is going to induce the growth of algae. Choosing a dark-colored tank is going to help with the algae problem, as it's going to prevent light from getting inside of the tank. However, dark colors absorb light, thus it can cause a dark-colored plastic tank to overheat.
Thick water tanks are stronger, so they are less likely to get damaged because of overheating. However, they are heavier and cost more than thin tanks do. Water tanks with reinforced ribs are also stronger, but their price is higher as well. The best solution is to keep the tank in a place with limited sunlight exposure.