When changing out the water for our tub, I consistly notice that the fresh water coming out of the hose has a subtle greenish hint to it. I researched this phenomenon a little and discovered that the area in which our city draws its water (fresh water lake) has been showing accelerated amounts of algae.
Thus the water, while safe to drink, comes with a slight hint of green. This phenonena is seen less in our parts in the fall/winter as opposed to the summer.
As for treatment - we just maintain our water as per usual. The greenish-hint slowly dissappears.
Hope this helps.
Jc