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.
Fluid Category 1
Description
Wholesome (drinking) water supplied by the water undertaker.
Example
Water supplied directly from a water undertaker's main.
Protection
- No additional backflow protection required for Fluid Category 1 itself.
Fluid Category 2
Description
Wholesome (drinking) water which has been changed, either heated or altered in taste, odour or appearance.
Example
Hot water.
Protection
- EA – Verifiable single check valve.
- EB – Non-verifiable single check valve.
Fluid Category 3
Description
Fluids posing a slight health hazard.
Example
Low-toxicity chemicals, such as common disinfectants.
Protection
- EC – Verifiable double check valve.
- ED – Non-verifiable double check valve.
Fluid Category 4
Description
Fluids posing a significant health hazard.
Example
Toxic substances, such as pesticides, and environmental organisms.
Protection
- An RPZ valve (where approved for the installation) or equivalent.
Fluid Category 5
Description
Fluids posing a serious health hazard.
Example
Pathogenic organisms, radioactive or very toxic substances, such as faecal matter.
Protection
- 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 information 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.