Water tanks are perched on top of the house, exposed to the full force of the sun, heat, rain, and windblown debris. Many older buildings, especially in cities with pre-war construction, use elevated tanks to keep water pressure for the upper floors, and those tanks are often the last thing anyone thinks about until the water coming out of the tap looks or smells wrong. 

Algae grows faster in direct sunlight inside the tank, and dust, insects, and bird droppings can enter through an open or poorly sealed lid. Because the tank is out of sight, problems often go unnoticed until water quality is affected throughout the building. 

Regular cleaning of your roof water tank will catch these before residents or tenants notice. This is one of the easiest maintenance items to forget about, as the tank itself is rarely seen from the ground.