What it is about
Part 4‑9 establishes WUE and its derived indicators, introduces three measurement categories, and sets out the rules for measuring, calculating, and reporting water usage in the operational phase. It is aimed at data center managers, operations managers, ICT managers, and general contractors.
The standard distinguishes between potable and non-potable water and between used and reused water; Category 3 additionally takes into account regional water availability and land use. The standard sets no limit or target value (EN 50600‑4‑9:2022, Introduction, Clauses 1 and 6.2.2).
Core requirements in our own words
WUE is an annual value in cubic meters per megawatt-hour of IT energy.
Water usage is the difference between water input and water output at the data center boundary; the ideal value is zero, and there is no upper limit. Both quantities apply to the same twelve months. Clauses 5 and 6.2.1.
Category 1 counts all water input as used.
Water for evaporation, cooling, and on-site energy generation is included; measuring the water output is not necessary. This is the basic level. Clause 6.2.2.2.
Category 2 credits non-industrial reuse.
Water that leaves the boundary and is used further outside reduces water usage; for this, the output must be measured. Clause 6.2.2.3.
Category 3 also accounts for the water used in energy generation.
Total energy consumption is multiplied by the energy supplier’s Energy Water Intensity Factor (EWIF); rainwater used on site is excluded. If the supplier does not provide an actual value, Category 1 or 2 applies. Clause 6.2.2.4, Annex C.
A report states the data center, the value, the category, and the end date.
In Category 3, the water stress indicator and land use are added; when published, the measurement points, the meters including their calibration, and the EWIF must be stated. Clauses 8.1.1, 8.1.2 and Annex B.
Derived indicators carry a prefix.
Interim “i”, partial “p”, design “d” with a joint plan for dWUE and dPUE, quality-related “q” for a single water quality, and peak WUE for one hour at full load in the design case; the Water Reuse Factor (WRF) complements the indicator. Clauses 8.4 and 8.5.
From our seminars: two misconceptions
“Water is not an issue for data centers in Germany.”
The indicator is part of the reporting obligations at every site: the Delegated Regulation requires water input and potable water input according to EN 50600‑4‑9, and the German Energy Efficiency Act (EnEfG) requires the efficiency indicator for water usage.
From seminar practice: as soon as adiabatic cooling comes into play, the water demand determines hygiene, inspection obligations, and the choice of system (Clause 7; Regulation (EU) 2024/1364, Annex II).
“Without evaporative cooling, our WUE is zero.”
In Categories 1 and 2, this is only true if no other function of the data center brings water across the boundary, such as humidification or cleaning. In Category 3, the water the supplier uses for electricity generation also counts; there is no meter on the building for this, but the supplier’s EWIF (Clause 6.2.2.4, Note 2).
Where Part 4‑9 applies in a project
Site and planning
Water availability, reuse potential, and the sealing of the site belong in site selection; the design WUE is planned together with the design PUE across the target IT loads (Clauses 7 and 8.4.5).
Legislation
The EnEfG requires operators to submit the efficiency indicator for water usage to the German energy efficiency register for data centers (Energieeffizienzregister) every year by 31 March (Section 13(1), Annex 3).
Reporting
Operators with an IT power demand of 500 kW or more report to the European database the total water input according to WUE Category 2, or alternatively Category 1, and the potable water input according to Category 1; the database calculates the WUE from these figures (Regulation (EU) 2024/1364, Annexes II and III).
This protects you from a report in which meters, category, and system boundary do not match (Clause 8.1.2.1).
Status and revision
- Current edition
DIN EN 50600‑4‑9:2023‑08, German edition of EN 50600‑4‑9:2022, approved by CENELEC on 12 December 2022; preceded by the draft E DIN EN 50600‑4‑9:2022‑05.
- International
ISO/IEC 30134‑9:2022; according to the European foreword, the European Standard is based on its content, and Commission Delegated Regulation (EU) 2024/1364 refers to both.
- Revision
no ongoing revision known. Committee CLC/TC 215, national mirror committee DKE/GK 719.
- Last reviewed
EN 50600‑4‑9
Frequently asked questions
The ratio of the annual water usage of the data center, in cubic meters, to the annual energy consumption of the IT equipment, in megawatt-hours (Clause 5).
For the European database, Category 2, or alternatively Category 1; the standard itself does not prescribe a category, but requires the chosen category to be stated as an index (Clause 8.1.1; Regulation (EU) 2024/1364, Annex II).
In Categories 1 and 2, rainwater used on site counts as non-potable water input; in Category 3, it is deducted so that the saving becomes visible (Clause 6.2.2.4).
The renewable freshwater per person and year at the site according to the Falkenmark indicator; in Category 3, it must be reported together with land use (Annex B, Annex D).
The standard recommends it, and on request of the authorities, the PUE value and PUE category must be available as evidence; for design values, a joint plan for dWUE and dPUE is required (Clauses 7, 8.1.2.2, 8.4.5).
Seminars
Related seminars
- DC-21008
Data Center Sustainability & Efficiency
5 days · In person
Water consumption of adiabatic cooling, environmental criteria such as the Blauer Engel ecolabel, and the indicators of the 4-x series with their system boundaries; this saves you a register submission with the wrong category.
Next date: 7–11 Jun 2027, Munich · GermanPrice plus VAT: €6,990 Training path 4/4
DC-21004Deep Dive – Power Supply & Cooling
according to EN 50600
5 days · In person · Live webinar
Adiabatic cooling, hygiene, and inspection obligations of evaporative cooling systems within thermodynamics.
Next date: 23–27 Nov 2026, onlinePrice plus VAT: €6,990
All prices plus VAT; the price is the same in every format.
- DIN EN 50600‑4‑9:2023‑08 (German edition of EN 50600‑4‑9:2022), national foreword of the German edition and European foreword, Introduction, Clauses 1, 3.1, 5, 6.1, 6.2, 7, 8.1 to 8.5, Annexes A to D
- ISO/IEC 30134‑9:2022
- Commission Delegated Regulation (EU) 2024/1364 of 14 March 2024, Articles 1 and 3, Annexes II and III
- German Energy Efficiency Act (Energieeffizienzgesetz, EnEfG) of 13 November 2023, Section 13, Annex 3
- DCE academy seminar practice: Data Center Sustainability & Efficiency (session November 2025), Data Center – General Principles (session April 2026), Deep Dive – Power Supply & Cooling (session November 2023)
Glossary terms
- Water Usage Effectiveness (WUE)
- water usage
- water input and water output
- potable and non-potable water
- industrial and non-industrial reuse
- Energy Water Intensity Factor (EWIF)
- Water stress and water availability (Falkenmark indicator)
- land use
- Water Reuse Factor (WRF)
- European database on data centers
