The quantity rH, an index of the reducing power of a redox system is, in co
nceptual and operational terms, coordinatively linked with the two familiar
electro-analytical quantities: redox potential (E-O/R) and pH, and has rec
ently become important in quality and environmental controls (hydrographic
network, human consumption waters, industrial effluents, etc.). It has some
significant problems of standardization and methodological applications, e
specially on passing from pure water medium to aqueous-organic media, and t
he results of the most recent researches are here presented.