I got really curious when, for the third time, I spent a few weeks in the US and my seborrheic eczema cleared up. It started to get irritated again every time I got back home. The water where I stayed was noticeably MUCH softer than my water at home so that got me thinking... and I found a lot of articles online that suggested hard water could aggravate skin conditions like eczema.
I acquired one of those filter jugs and I've been washing my face and scalp with the filtered water for the past month. I'm wary of speaking too soon but the difference is huge! My skin has been sooooooooo much less irritated for the past month using this filter, flakiness is much improved and the redness across my cheeks has gone down enormously. I really think it must be the water, because nothing else has changed. :)