How Does A Water Tank Become So Dirty?

It does not matter how clean the water arriving the water tanks is (even if it came from a purifying machine), after 4-6 months they are taken to the tanks, as a result of physical and chemical reactions, the substances in the water such as iron, manganese and lime depart from the water forming a layer of pollution in the tanks and containers.

City waters that are not fully purified and environmental waste water that infiltrate through hidden pipe cracks with reverse vacuum and kittens, mice, dead insects that we see at the tanks and warms and maggots turn our tanks into a microbe nests.