A. The Water Supply (Water Fittings) Regulations and Scottish Water Byelaws require domestic water supplies to be adequately protected from backflow.

These regulations and byelaws define Fluid Risk Categories by the type of contaminants which may be present, and take into account the risk of harm to human health which may be caused. They also specify appropriate types of prevention devices which must be fitted to guard against backflow.

Backflow prevention devices must be fitted between the domestic plumbing system and the source of the potential contamination.

The table below give a simple overview of the fluid categories and typical backflow protection devices which could be used.

Please note this is not a comprehensive or exhaustive list.

 Fluid Category – risk to health

 Typical device which may be used

 1. – drinking water - no risk

 No backflow prevention device needed

 2. – slight change in taste, odour or  temperature – slightly unpleasant

 Single check valve

 3. – chemicals of low toxicity – slight health  hazard

 Double check valve

 4. – toxic chemicals or carcinogenic  substances – significant health hazard

 Reduced Pressure Zone (RPZ) valve or  break cistern incorporating a Type AF air  gap

 5. – radioactive or very toxic substances,  faecal and pathogenic organisms – serious  health hazard

 Break cistern incorporating a Type AA or AB  air gap

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