the amount of oxygen dissolved in a body of water as an indication of the degree of health of the water and its ability to support a balanced aquatic ecosystem; also, the amount of free (not chemically combined) oxygen dissolved in water, wastewater, or other liquid, usually expressed in milligrams per liter, parts per million, or percent of saturation; abbr. DO
In the absence of dissolved oxygen, the bacillus appears to take its iron from the pipes.
This dissolved oxygen can easily combine with the dissolved iron; the solution helps the chemical change to take place.
In the case of metallic copper this action has been attributed to oxidation induced by the dissolved oxygen in the copper.