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

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 gives a simple overview of the fluid categories and typical backflow protection devices which could be used.

Fluid category (FC) - 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
Please note this is not a comprehensive or exhaustive list. 

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