The “color,” or the “true color,” of water shall be considered the color
that is due only to substances in solution; that is, it is the color of
the water after the suspended matter has been removed. In stating
results the word “color” shall mean the “true color” unless otherwise
designated.
The “apparent color” shall be considered as including not only the true
color but also any color produced by substances in suspension. It is the
color of the original unfiltered sample.
The platinum-cobalt method of measuring color shall be considered as the
standard, and the unit of color shall be that produced by 1 part per
million of platinum.