The green goo mystery is solved!

Back in February 2016, I wrote about water quality and a recent phenomenon occurring here in Southern California on some of my projects. Green gelatinous globules (green goo) has been showing up in the hot water supply in certain buildings. The goo gets clogged in lavatory aerators and valve strainers such that it severely retards the flow rate to these fixtures. Image 1 shows what it looks like after draining a bathtub.

 I posted a blog with ASPE about this back in June, and a post was also made on Plumbing Engineer's social media, in hopes that someone out there knew the source to this problem. But, I did not get an all-knowing reply. As I noted last February, the building where this was occurring is a multi-million dollar condominium high-rise with very low occupancy. The hot water zones are circulated through commercial storage tank booster heaters continually, while hot water demand is quite small. The owners in this building are those with multiple homes and only spend a small fraction of their time in this building. The phenomenon was also occurring in another low-rise condo project, but not to the extent as in the high-rise.

Working with multiple engineers and water quality specialists, we put our heads together to try to figure out why this was happening. The aspects of SoCal water that make it quite unique are the combination of elevated hardness and the use of chloramine as a disinfectant, but these elements don’t explain the green color of the goo.

Certain elements cause associated colors to form in chemical reactions. Copper oxide is green of course (i.e. the Statue of Liberty), but if this green stuff was a copper reaction, why was it happening, and why wasn’t it happening in all buildings? A water analysis indicated that the copper levels in the water were not high so it couldn’t be a copper reaction that was happening here. Calcium and magnesium levels were high, but that is always the case with our hard water.

After my February article, I received a comment from a reader that the green color can be created by a magnesium anode rod in the water heaters. I found it hard to believe that a small anode rod in a system this large could produce the amount of green goo that we were experiencing in the building, but I didn’t dismiss the possibility. I bounced this idea off our water quality specialist, and he said yes, magnesium can show up as green. So, the theory started to develop that the green material could be a combination of calcium and magnesium from the anode rod, perhaps in reaction with the chloramines.

I suggested removing the anode rods as a test, but the manufacturer said that would void the warranty if we did so. I knew that anode rods also came in aluminum, so I suggested replacing the magnesium with aluminum and we put that theory to test.

In the meantime, while the building was in shutdown mode, we decided to add a water softener to soften the hot water before it returned to the booster heaters with the anode rods. The theory being that if the calcium were reacting with the anodes and chloramines, that getting rid of the calcium before it hit the anode rods might prevent the reaction.

With the aluminum anode rods and water softener installed, we flushed the piping and tested the water by flowing it from various fixtures, the results of which you can see in Image 3. The goo turned from green to white, but was still present and sufficient in quantity to clog aerators and screens. However, the amount of it seemed to reduce considerably, but that was not good enough for a clean system.    

Finally, the building owner agreed to remove the anode rods completely from the heaters, warranty be damned. After another flush and test, the system was finally running 95 clean (image 4), and the remaining five  percent was probably residual from debris that was in the piping before the anode rods were removed.

So it seems the solution to this mystery requires the anode rods to be left out permanently, but is that practical? I asked the question, with dielectric fittings on both water connections to the heater, what is the purpose of the anode rods? I was told that the anode rods help protect the tank from minor imperfections in the tank lining. I’m not sure I understand that. I don’t understand the chemistry of how an anode rod would keep the tank from rusting if the tank lining had an imperfection. But, that’s their story, and they’re sticking to it. 

Timothy Allinson is vice president of Engineering at Murray Co., Mechanical Contractors, in Long Beach, California. He holds a BSME from Tufts University and an MBA from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a LEED accredited professional. Allinson is a past-president of ASPE, both the New York and Orange County chapters. He can be reached at

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