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When ‘white sand’ isn’t as good as it sounds

While for most of us the words ‘white sand’ bring up images of the Bahamas and paradise shores, for an unfortunate few, white sand means they have an issue with their plumbing systems.

Water companies across the country have reported a ‘white sand’ type substance at cold water outlets  - commonly bathroom taps and toilet cisterns - that was not apparent at the cold kitchen tap.  In these cases, there was no cold water storage at the premises (i.e. the cold water outlets were mains-fed) and the hot water was supplied from an unvented cylinder.

Paul Millard, Technical Manager of WRAS stated that further “laboratory analysis of the ‘sand’ confirmed that it was lime scale (calcium carbonate) and investigations identified the most likely cause was that it had collected at the bottom of the unvented cylinder and been drawn back into the cold water supply.”

So if you are a plumber investigating a case of white sand at a client’s property, what should you be aware of? Paul offered the following points:

  • Remember that plumbers require a specialist qualification to install and undertake maintenance on unvented cylinders. So only do work you are correctly qualified to undertake.
  • In accordance with the installation instructions, the draw off point for cold water outlets should be before the non return valve for the cylinder.
  • The non return valve contains back-flow protection that will prevent water from inside the cylinder being drawn back into the incoming cold supply.
  • In the cases reviewed the draw off point had been installed downstream of the non return valve, hence it was possible for lime scale from the cylinder to be drawn back into the cold water.
  • The incorrect installation of unvented cylinders can result in water quality issues for consumers.

For more information on WRAS visit