You must’ve seen water tanks, maybe you even have one on the roof of your building itself. But have you thought about how most of the overhead tanks are printed black? No, it’s not because the manufacturers are lazy or because your father really likes The Rolling Stones. There’s a science behind it and that is what we are going to look at in this article.

Why water tanks are black?

Water tanks are often painted black or made of black materials because black surfaces absorb and retain heat more effectively than lighter colors. By making water tanks black, they can absorb solar radiation more efficiently. Sunlight also promotes the growth of algae in water. By using black tanks, which reduce the penetration of light into the water, the growth of algae can be minimized.

Before we discuss that, let’s first understand why stagnant water is problematic. Stagnant water, under the exposure of sunlight, promotes algae growth. This is often seen in ponds where the water surface is covered with Chlorophyceae (a type of algae). Water infested with algae, other than being gross, can also cause various health problems if drunk or bathed in. Hence, it is imperative that algal growth is hindered in the water that is to be used for domestic and drinking purposes.

Now, one of the ways to check algal growth in water is by blocking out the sunlight. This is where the black paint comes in. The colour black is a great absorber of sunlight. Hence, it prevents most of the sunlight from reaching the interior of the tank, thus preventing algal growth. The flip side to this practice is that the black paint also increases the temperature of the stored water by a large margin, thus being an annoyance during the summers.

It's important to note that the choice of tank color can also depend on specific local conditions and requirements. For example, in very hot and sunny climates, black tanks may be used to maximize solar heating, whereas in colder climates, darker colors may be preferred to assist in maintaining water temperature. However, in some cases, tanks are insulated or placed underground to minimize heat gain or loss.

Why are water tanks cylindrical?

Cylindrical water tanks distribute water pressure uniformly, maximizing structural integrity. The shape also minimizes material usage and simplifies manufacturing, installation, and maintenance processes, making it a practical and efficient design.