RESOURCES
UV Dose Reference Chart
Required UV fluence (mJ/cm²) for pathogen inactivation in water treatment — from 1-log to 4-log. Based on WHO GDWQ, US EPA LT2ESWTR, and IUVA validated data.
UV Fluence (Dose)
Energy delivered per unit area: mJ/cm² = mW/cm² × seconds. Higher fluence = more pathogen inactivation.
Log Inactivation
1-log = 90% kill, 2-log = 99%, 3-log = 99.9%, 4-log = 99.99%. US EPA LT2ESWTR awards log credits.
UV Transmittance (UVT)
% of UV light passing through 1cm of water at 254nm. Low UVT (turbid/coloured water) requires higher lamp power.
UV Dose by Pathogen (mJ/cm² at 254nm)
| Pathogen | Type | 1-log | 2-log | 3-log | 4-log | Source |
|---|---|---|---|---|---|---|
| Cryptosporidium parvumKEY Chlorine-resistant; UV is the primary control. US EPA LT2ESWTR awards 2-log credit at 5.8 mJ/cm². | Protozoa | 1.6 | 3.2 | 6.3 | 12 | US EPA LT2ESWTR (2006) |
| Giardia lamblia UV at 10 mJ/cm² achieves >3-log inactivation. More sensitive to UV than Cryptosporidium. | Protozoa | 1.5 | 2.1 | 3.3 | 6 | US EPA UVDGM (2003) |
| E. coli Highly UV-sensitive. 4-log kill achieved at <10 mJ/cm². Standard indicator organism for water quality. | Bacteria | 1.5 | 3 | 5.5 | 8.5 | WHO GDWQ 4th Ed. (2017) |
| Faecal coliforms CPCB treated sewage reuse standard: <100 MPN/100mL. UV at 25 mJ/cm² reliably achieves CPCB limits. | Bacteria | 1.5 | 3 | 5 | 8 | CPCB GNSS 2015 / WHO |
| Legionella pneumophila UVGI (UV germicidal irradiation) in AHU ducts uses 15–25 mJ/cm² for HVAC Legionella control. | Bacteria | 1.3 | 2.5 | 4 | 6.5 | ASHRAE 188 / IUVA |
| AdenovirusKEY Most UV-resistant human virus at 254nm. Polychromatic UV (LP + MP) or 222nm Far-UV recommended for adenovirus control. | Virus | 40 | 80 | 120 | 160 | US EPA UVDGM (2003) |
| MS2 Bacteriophage (surrogate) Used as challenge organism in US EPA reactor validation testing for virus inactivation credit. | Virus (surrogate) | 14 | 28 | 54 | 108 | US EPA UVDGM (2003) |
| Rotavirus More UV-sensitive than adenovirus. 40 mJ/cm² achieves >4-log reduction. | Virus | 9 | 18 | 36 | 72 | WHO GDWQ 4th Ed. |
| Pseudomonas aeruginosa Biofilm-forming; important in hospital water and cooling tower control. UV at 15 mJ/cm² achieves 3-log reduction. | Bacteria | 2 | 3.9 | 7.9 | 15 | IUVA / WHO |
| Mycobacterium (non-tuberculosis) Relatively UV-resistant. Found in cooling towers and building water systems. ASHRAE 188 WMP target. | Bacteria | 5 | 10 | 20 | 40 | IUVA Guidance |
All values for low-pressure mercury UV lamps at 254nm. Medium-pressure polychromatic UV achieves higher doses at equivalent power for virus control. UVT assumed ≥85%. Values are guidance — reactor-specific validation required for regulatory compliance.
Regulatory UV Dose Requirements
| Standard / Regulation | Minimum UV Dose | Target | Application |
|---|---|---|---|
| US EPA LT2ESWTR | 2.5 mJ/cm² | 0.5-log Cryptosporidium credit | Filtered surface water |
| US EPA LT2ESWTR | 10 mJ/cm² | 2-log Cryptosporidium credit | Filtered surface water |
| US EPA LT2ESWTR | 40 mJ/cm² | 3-log Cryptosporidium credit | Unfiltered surface water |
| WHO GDWQ 4th Ed. | ≥25 mJ/cm² | Drinking water safety goal | Point-of-use to municipal |
| BIS IS 10500:2012 | ≥16 mJ/cm² | E. coli not detectable | Indian drinking water |
| FSSAI Food Safety | ≥25 mJ/cm² | Process water for food contact | Food processing plants |
| CPCB STP reuse | ≥25 mJ/cm² | <100 MPN/100mL FC | Treated sewage reuse |
| ASHRAE 188 (UVGI) | 15–25 mJ/cm² | Legionella 3-log in HVAC | AHU / cooling tower |
| NABL / NABH hospitals | ≥30 mJ/cm² | Sterile water / instrument wash | Healthcare facilities |
UV System Sizing Guide
Indicative lamp wattage for water flow at 25–30 mJ/cm² (drinking water standard), UVT ≥85%. Actual sizing depends on reactor design and validated flow rate.
| Flow Rate | UV Dose Target | Lamp Power (indicative) | Typical Application |
|---|---|---|---|
| 100 LPH | 25 mJ/cm² | 4W | Point-of-use drinking water |
| 500 LPH | 25 mJ/cm² | 16W | Small commercial / restaurant |
| 2,000 LPH | 25 mJ/cm² | 55W | Small industry / hotel |
| 10,000 LPH (10 m³/hr) | 30 mJ/cm² | 250W | Industrial process water |
| 50,000 LPH (50 m³/hr) | 30 mJ/cm² | 1.2 kW | Municipal WTP / large ETP |
| 200,000 LPH (200 m³/hr) | 40 mJ/cm² | 4.5 kW | Large municipal WTP |
UV lamp power assumes LP mercury vapour lamps at 85% UVT. For low-UVT water (<70%) or virus inactivation targets, increase lamp power by 1.5–2×. Contact us with your flow rate and UVT for accurate sizing.
Ozone vs UV — When to Use Which
| Parameter | Ozone | UV Disinfection |
|---|---|---|
| Primary mechanism | Chemical oxidation | DNA/RNA damage (photolysis) |
| Residual disinfection | Yes (short-lived, O₃ decays to O₂) | No residual — must re-dose on recontamination |
| Cryptosporidium | Effective (CT 5–10 mg·min/L) | Very effective (10 mJ/cm²) |
| Adenovirus | Effective at standard dose | Requires high dose (>40 mJ/cm²) |
| Biofilm / organic removal | Excellent — oxidises organics | None — does not remove organics |
| Chemical byproducts | Bromate (if bromide present) | None |
| Operating cost | Moderate (compressor + power) | Low (lamp + power only) |
| Best for | STP/ETP, colour, taste/odour, biofilm | Final polish, cold-chain, pharmaceutical |
Many municipal and industrial water treatment plants use ozone + UV in sequence: ozone for primary disinfection and organics removal, UV for final pathogen control before distribution. View our UV water treatment systems →