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 painted 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.

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.