A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials. Many engineers in the water treatment industry confuse “available chlorine for chlorine that is capable of oxidizing things and not already minimized by other reactions. Although this thought process is not entirely wrong, it is not always correct. Available chlorine more closely resembles a tool of common testing parameters. It is frequently used as a metric to determine the fraction of orhotolodine (OTO) and diethyl phenylenediamine (DPD), which are both chlorines that closely resemble each other, unless there are other salts present such as iodide or bromide.