What does the term 'Gain' refer to in the context provided?

In the context of water treatment, the term 'Gain' is best understood as a net increase after treatment. This refers to the positive effect achieved as a result of the treatment process, such as improving water quality, removing contaminants, or increasing the volume of usable water. The concept encompasses not only the quantity of water treated but also the efficacy of the treatment methods employed, leading to an enhanced or improved end product.

While initial setup, final measure of output, or pre-last may relate to various aspects of the process, they do not encapsulate the overall effectiveness demonstrated by 'Gain.' The focus is specifically on the increase resulting from the treatment, which emphasizes the outcome rather than the process or setup stages.