I haven't looked deeply into urine porphyrin testing, Ellasmom may know more.
What I think is, a urine porphyrin test should tell you if you have enough of several heavy metals (I think it's more than just mercury, but I haven't focused as much there), then your body will start maladapting in such a way as to show up on the test. So it's not so much a matter of what the source is, it's whether it's hanging around in your body causing trouble.
Your urine porphyrin test came back fine? Did they send it off to France? I hear many labs aren't reliable, but there's one in France that is (Ellasmom would know which one, it's where they're sending Ella's urine sample).
That said--can you just test the water? I'm guessing that's more complicated than I'm thinking? Or do you think something changed, so that the water was suspect in the past but now is good?
Or are you wondering if another source of metals may exist? Your low glutathione isn't great (from your OAT), do you think that's just dietary?
Hair is so nice because it's so non-invasive. I don't know how to interpret DMSA provocation tests, and I guess they scare me because I'm using DMSA very specifically, and carefully, to pull out metals. It scares me to take a whole lot at once and then just let the chips fall where they may, in terms of resettling.
Do you know what, specifically, he's looking for? Does he want to focus on particular metals (or figure out if it's A or B), or he thinks there's something big that's been the underlying cause of the gut dysbiosis?