Rainwater quality depends upon the free circulation of air within the collection and storage system. Allowing the air to move freely through the system will maximize the oxygen contact with the water. Removing the particles by pre-filtration and calming the water as it enters the tank will provide clear water free of suspended solids. Drawing water from just below the surface of the tank will ensure that the cleanest water is always removed from the tank. A properly constructed overflow will help skim the surface of particles and films that may float to the surface.