Water industry calculators
Flow, pipe volume, legionella temperature bands and fluid category reference for UK plumbing revision — verify on site with current standards.
Flow rate (l/s)
Q = A × v — enter internal diameter (mm) and velocity (m/s). Typical design velocities ~0.9–1.5 m/s for small bore revision.
Pipe volume & fill time
Volume = π × (d/2)² × length. Useful for disinfection/flushing estimates.
Legionella temperature band
HSG274-style revision bands — follow your site risk assessment on real systems.
- < 20 °C — growth very slow in wholesome cold (avoid stagnation).
- 20–45 °C — favourable for Legionella proliferation.
- 50 °C+ — kills most bacteria given time.
- 60 °C — commonly cited for stored hot water pasteurisation.
Fluid categories 1–5 (reference)
Higher category → stronger backflow protection. Search this table in open-book exams.
| Cat | Meaning | Examples | Typical protection theme |
|---|---|---|---|
| 1 | Wholesome undertaker supply | Mains cold water | Baseline supply — protect downstream |
| 2 | Aesthetic change only | Heated wholesome, mixed temperature | Check valve / air gap per risk assessment |
| 3 | Slight health hazard | Some process fluids, light chemicals | DCV or stronger |
| 4 | Significant toxic hazard | Industrial chemicals | RPZ, air gap or break tank |
| 5 | Serious health hazard | WC pan, urinal, drains, hospital waste | Strongest suitable device |