So you’ve decided to buy a tank for collecting and storing rain water? Or maybe you’d like to keep a full water storage tank on hand for emergencies? Whatever the reason, knowing more about the key features of plastic storage tanks can help you hone in on the right one for your needs during the decision making process.
Tank Features to Consider
Color: Water storage tanks are typically made available in darker hues, i.e. black or dark green. This is because water can contain algae and bacteria, which are light sensitive. Exposing them to sunlight catalyzes their growth in water. The darker colors prevent sunlight from getting into the tank, which in turn inhibits algae growth. Though most algae are not a human health risk, they adversely affect the taste, odor, and color of the stored water.
Illustration: Black and Green color tanks
Ultra violet (UV) protection: Prolonged exposure to the UV radiation in sunlight will cause the degradation of unprotected plastic tanks. This deterioration affects the physical properties of the tank, leading to discoloration, cracking, and loss of strength. When UV stabilizers are added to the polyethylene resin during the tank’s production, the plastic structure becomes protected from the effects of UV radiation, which increases the durability of the tank.
Bisphenol A (BPA) free: BPA is an industrial chemical used to harden plastics and has found its way into many plastics based containers. BPA can leach into the contents of the plastic container, and if ingested, it can cause adverse health issues. To protect yourself, opt for plastic tanks made from BPA free polyethylene resins.
Specific Gravity: In addition to the capacity (how many gallons they hold), tanks are also rated by the specific gravity of the substance that they are designed to contain. Specific gravity is the ratio of the density in kilograms per cubic meter of the substance to the specific gravity of a reference liquid (usually water). A tank built for storage purposes needs to be thick enough to withstand the weight of the liquid that it is storing. A thicker size indicates a higher specific gravity. A tank that proves too light for the liquid within it will ultimately break. For reference, a tank designed to be used for water storage applications will generally have a specific gravity of one.
The tanks designed for underground storage applications have a higher specific gravity (close to 2) since they not only have to withstand internal water pressure, but also contend with the external soil pressure. Similarly, tanks with higher capacities generally have higher specific gravity ratings. A higher specific gravity, or thickness, is achieved by adding more resin during the manufacturing process. This explains why the cost for these tanks is higher as well.
Illustration: Underground storage tanks
Inlet and outlet provision: Tanks will generally have both an inlet and an outlet provision for the water to enter into and drain out from the tank. In addition, the tanks may also have a provision for excess water overflow, or human access into the tank for cleaning. The provision for human access is a manway/ manhole of an appropriate diameter. In bigger tanks with underground storage applications, there may be two manways since the tank shape is horizontally cylindrical. The two manways (one on either end of the tank) provide access for cleaning.
Illustration: Tank inlet and outlet provisions
Shape: Vertical cylindrical tanks are ideal for above ground water storage purposes while horizontal cylindrical tanks are more appropriate for underground storage applications. Horizontal cylindrical tanks with legs acting as baffles are great for use as transportation tanks. The baffles prevent the liquid inside the tank from sloshing while it is being transported.
Illustration: Water Transportation tanks with baffles