Backflow Protection: FAQs
What is a fluid category?
Schedule 1 of the water fittings regulations in England, Wales and Northern Ireland, byelaws in Scotland, classify the health risk posed by potential contaminants using a scale called fluid categories.
There are five fluid categories in total the lowest being 1 no risk the highest 5 a serious health hazard.

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1
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Wholesome (drinking) water supplied by the undertaker
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water direct from a water undertaker’s main
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2
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Wholesome (drinking) water which has been changed either heated or altered in taste, odour or appearance
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Hot water
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3
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Fluids posing a slight health hazard
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low toxicity chemicals such as common disinfectants
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4
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Fluids posing a significant health hazard.
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Toxic substances such as pesticides and environmental organisms
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5
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Fluids posing a serious health hazard
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Pathogenic organisms, radioactive or very toxic substances such as faecal matter
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Disclaimer
Uncontrolled if downloaded. This is informative, non-statutory guidance and intended for general guidance purposes only; it is subject to change.
Compliance with this information should not be relied upon as guaranteeing no enforcement action will be taken by water undertakers. Water Regs UK accepts no liability for loss, indirect or consequential loss arising from or in connection with this guidance document.