Within months of completion, personnel at a large institutional facility in the Midwest began to observe water quality concerns. Reports to the building owner included sinks that had brown-colored water, green-colored water and even one location where the water ran clear initially, then ran rusty and discolored, and then ran clear again. Mysteriously, this only happened on Monday mornings and only on the hot water side. The owner was mystified and called Crane Engineering to help unravel the mystery of the unclear water.
As bulk water travels through a distribution network, typically through metal pipe, it undergoes various chemical, physical and aesthetic changes that impact water quality. These changes may include water chemistry, temperature, piping materials, velocity, water age (how long the water resides in a pipe), galvanic couples, and bacteria, to name only a few.
After a thorough water system examination, water testing and metallurgical examination of various pipes, valves and dielectric unions, the underlying root causes of this complicated problem were determined.
The system had been oversized for future expansion, which made for long water residence time in the building, (greater than 14 days in some locations). This should be less than a day or two typically. Water treatment during building construction had been inadequate and dielectric unions were lacking in many locations, which led to galvanic corrosion.
The following is a video of the Monday morning hot water faucet in question, along with an animation created to tell the “rest of the story”, which occurred behind the walls in the water piping system over the weekend.
Rusting had occurred due to galvanic corrosion in the hot water recirculation system. This rust accumulated in a long vertical leg and concentrated at the bottom of the short horizontal run over the weekend and during periods of extended inactivity.
When the faucet was turned on, the water retained in the faucet was clear, but a slug of rusty water followed shortly thereafter.
Numerous changes were made to the system to correct these problems. These included removal of cast iron strainers, adding automatic valves to run the water in low use areas each evening, and replacing dielectric nipples (plastic lined metal pipe sections) with dielectric unions, to electrically insulate adjacent pipe segments.
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