BLUE WATER IN THE DESERT


By: Russell M. Keeler, PE

In a residence recently built in New Mexico, a strange phenomenon was observed when the house was completed; domestic water in the house was blue in color, undrinkable, had a slippery feel, and caused skin irritation.  The house was connected to the local water utility piping system, and was the only building on the block to exhibit the toxicity.  The only difference between this house and the others on the block was that it used PEX  tubing instead of copper domestic water piping.  The PEX tubing used in this installation was an aluminum tube between two layers of polyethylene.
My investigation included a field survey, which showed a gray powder deposit at some of the brass fittings in the piping system.  Chemical analysis disclosed that this powder was zinc hydroxide.  Research indicated that a phenomenon called “zincification” can take place with compounds of zinc and copper when exposed to water with a high pH.  Brass fittings were used to make tee and elbow connections to the tubing.  The brass used is an alloy of copper and zinc.  Connections between the fittings and the tubing were made using a crimping tool.  The fitting is inserted into the tubing and a tight fit is made by pressure from the crimping tool.
Findings were as follows:
  1. The high pH of the municipal water in contact with the brass fittings in the PEX plumbing system set up the process of dezincification.  Zinc hydroxide crystals were observed in the vicinity of a brass fitting.
  2. There was aluminum to brass contact, creating a galvanic action that would help drive the zinc into solution.
  3. Removal of the zinc from the brass fittings has “dealloyed” the fittings to the point that only copper remained in the fittings, and in a condition of little strength.
  4. Not only had the high pH water caused the dealloying of the brass fittings, but the water also serves as an electrolyte.
  5. Once the fittings became generally copper, the electrolyte served to create galvanic activity.  Copper ions go into solution as part of the dezincification process.
  6. The hydrogen ions in the high pH water have combined with the copper ions in solution to form copper hydroxide.
  7. This final product of the process, copper hydroxide, was the cause of the blue water and its resultant smell, taste, color and slippery feel.
In order to correct the problem, it will be necessary to replace the brass fittings with either plastic or copper fittings.  Manufacturers of PEX tubing should alert installers to use either plastic or copper fittings where water has a high pH.

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  polyethylene
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