I was first introduced to black water in 1972 as an apprentice at F. W. Behler, where I had just begun the never-ending learning curve. We were draining a hydronic hot water system that served a large row home with standing cast iron radiators. The water was dark colored and smelled a bit funky, but it was explained, to me, that this was perfectly normal and highly desirable because that indicated the hydronic water was essentially devoid of free oxygen.
I was fortunate to be hired at Behler because they performed lots of hydronic work servicing and replacing tons of stem and hot water boilers. The older gentlemen I was working with had decades of experience and were eager to teach this young lad the proper ways of servicing/installing all things plumbing, heating and air conditioning related. The owners, Herb Behler and Scott Behler, were third-generation owners. Their grandfather had started the business in the late 1800s and relocated to York, Pennsylvania in 1900. The end result was many of the hot water and steam systems we worked on had been installed by Behler crews. I learned from these old salts that when first filled and purged, water in a hydronic system contains free oxygen that readily and aggressively attacks ferrous materials, and basically the whole system was comprised of ferrous items: Cast iron boiler; black iron piping; and standing cast iron radiators. What’s not to rust?