Oh Ben, you are so patient with us novices. Well, would you believe that we do not have well water? It actually does come to us treated. Though, it does make sense that iron tests only measure dissolved iron and maybe that's why our levels seem low. I did do the bucket test on pre-softened water, but it did go through a sediment filter 1st - one of those that looks like yarn wrapped around a tube - which obviously gets overwhelmed quickly, hence all the sediment. Anyway, I think I will have my husband climb into the crawl space to get us some unfiltered water to do a bucket test, just to see. And in the meantime we'll keep filtering!