Join Date: Jul 2013
Location: Gainesville, FL
My background is in environmental water quality, so to be honest I don't have a good grasp on how it's used for utility water treatment.
Phosphates will readily bind with different metals depending on the pH. Like you said, the idea is that it forms a coating on your pipes when it precipitates with heavy metals (Pb, Cu, etc.) or even lighter metals (Fe, Mn, etc.) that are less regulated but can still be annoying.
My assumption, however, is that it is likely added in slight excess. Depending on how they add it, either as a phosphoric acid or a phosphate salt, you will likely end up with some of that in your tap. But that could totally be wrong!
I misread that it was the dosage quoted above as in that is what they are adding, in which case it shouldn't be exactly what comes out of your tap since the coating should be insoluble (otherwise it's not working), not what they're projecting as coming out of the tap.
Might be something to monitor but I can't imagine it's going to be causing major problems since it's still safe to drink. I'd only slightly be concerned that if they are dosing when there, for whatever reason, aren't a lot of metals to bind with it that you happen to add a decent amount of P all at once during a water change.