Fluid Categories 1–5 Explained
UK water regulations classify fluids by the level of risk they pose to the water supply. The fluid category at your premises determines the backflow protection required.
| Category | Risk | Typical protection |
|---|---|---|
| Category 1 | Wholesome water supplied by the water undertaker | No backflow protection normally required. |
| Category 2 | Water that would be wholesome but has changed in taste, odour or temperature | A single check valve (type A) or equivalent is generally suitable. |
| Category 3 | Water with a slight health hazard, e.g. common food or mild contaminants | A double check valve (type A) or equivalent is generally suitable. |
| Category 4 | A significant health hazard, e.g. concentrated chemicals or biological agents | An RPZ valve (where approved for the installation) or equivalent. |
| Category 5 | A serious health hazard, e.g. human waste, pathogens from medical use | An air gap or equivalent is normally required. An RPZ valve may be used for category 5 only with written consent from the water undertaker. |
This table is a general guide. The correct protection depends on the specific installation and the requirements that apply. We confirm the right device during a site assessment.
Why the category matters
Choosing a device that does not match the fluid category leaves your premises non-compliant and the water supply at risk. Equally, over-specifying protection adds unnecessary cost. We help you identify the actual risk on site and specify the correct, compliant solution.