减/減 (Reduce/Subtract/Decrease/Diminish): What's it got to do with water?
I think both "減" and "咸" exists in the ancient times, but for certain reasons scholars like to use "咸" in place of "減".

損也,從水,咸聲 == It has the same meaning as '損', water as glyph component, and the same pronunciation as '咸'.

In 管子·宙合, which was written before the early Han Dynasty, it says "左操五音，右執五味，懷繩與准鉤，多備規軸，減 溜大成，是唯時德之節。 .... 減，盡也。溜，發也。 ...."