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* Part of: [[Measurement:Main_Page]]
* Part of: [[Measurement:Main_Page]]
* Related to: [[Measurement:Units]]
* Related to: [[Measurement:Units]]


AOWIS is based on the International System of Units (SI), as specified in [[Measurement:Units|Units]]. Accordingly, AOWIS uses UCUM<ref name="UCUM">Unified Code for Units of Measure (UCUM) https://ucum.org</ref> as the normative syntax and code system for machine-readable unit identifiers.
This page is the normative registry of canonical measurement quantities and units used by AOWIS.
 
The representation and conversion rules governing these quantities are defined in [[Measurement:Units]].


AOWIS defines a canonical set of UCUM unit identifiers used across all system interfaces, storage formats, APIs, and inter-system data exchanges.
UCUM<ref name="UCUM">Unified Code for Units of Measure (UCUM) https://ucum.org</ref> is used for machine-readable physical unit identifiers.


Unit identifiers are machine-readable tokens and are not intended to represent typographic or human-readable SI notation.
== Identifier and Field-Naming Rules ==


== General Rules ==
The canonical unit assigned to each measurement quantity in this registry is authoritative.


* All unit identifiers MUST conform to UCUM.
When a unit identifier is explicitly represented, it MUST use the canonical UCUM identifier defined here.
* Each measurement quantity MUST be assigned exactly one UCUM unit identifier as its canonical unit identifier.
* Canonical unit identifiers MUST be used consistently across all AOWIS-compliant systems, interfaces, storage formats, APIs, and inter-system data exchanges.
* Canonical unit identifiers MUST be interpreted independently of locale, display format, implementation, and system context.
* Canonical unit identifiers MUST remain stable across AOWIS-compliant systems and data formats.


== Requirements ==
The AOWIS identifier suffix is an ASCII-safe naming convention used for fixed-schema field names, property names, database columns, and similar technical identifiers.


<pre>
The suffix convention is:
REQ-MEAS-UNI-001: All unit identifiers MUST conform to UCUM.


REQ-MEAS-UNI-002: Each measurement quantity MUST be assigned exactly one UCUM unit identifier as its canonical unit identifier.
* division is represented by <code>_per_</code>;
* multiplication is represented by <code>_</code>;
* unit symbols are normalized to lower case where required for identifier naming;
* quantity-specific semantic qualifiers MAY be included where a literal unit-only suffix would be ambiguous;
* dimensionless fields with canonical UCUM unit <code>1</code> normally omit a unit suffix.


REQ-MEAS-UNI-003: The canonical unit identifier assigned to a measurement quantity MUST be used consistently across all AOWIS-compliant systems, interfaces, storage formats, APIs, and inter-system data exchanges.
For example:


REQ-MEAS-UNI-004: The measurement quantity identifier defines what is measured, while the unit identifier defines the unit in which it is expressed.
<pre>
m3/h        -> m3_per_h
m/s        -> m_per_s
kW.h/m3    -> kw_h_per_m3
mm2/(100.m) -> mm2_per_100m
</pre>
</pre>


== Canonical Measurement Quantities and Units ==
The AOWIS identifier suffix is not itself a UCUM unit identifier.


=== Length and Spatial Quantities ===
For generic or dynamically typed measurement values, the resolved measurement quantity determines the canonical unit through this registry.
 
== Length and Distance Quantities ==


{| class="wikitable"
{| class="wikitable"
! Quantity / Name !! Definition !! Canonical Unit (SI symbol) !! Serialized Unit !! EPANET Mapping
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
|-
| length || Linear spatial extent || m || m || Pipe/link length (SI-normalized EPANET model)
| <code>length</code> || Linear spatial extent along an object or path || metre (m) || <code>m</code> || <code>m</code> || Pipe and link length
|-
|-
| elevation || Vertical height relative to datum || m || m || Node elevation (SI-normalized EPANET model)
| <code>elevation</code> || Vertical height relative to an engineering or hydraulic datum || metre (m) || <code>m</code> || <code>m</code> || Junction, tank, reservoir, and terrain elevation
|-
|-
| distance || Spatial separation between points || m || m || Derived geometric quantity
| <code>altitude</code> || Vertical position reported by a geographic positioning source || metre (m) || <code>m</code> || <code>m</code> || Geographic altitude; not necessarily suitable as hydraulic elevation
|-
|-
| position_offset || Relative spatial offset magnitude || m || m || Not explicitly represented in EPANET
| <code>distance</code> || Spatial separation between positions || metre (m) || <code>m</code> || <code>m</code> || Derived geometric distance
|-
| <code>vertical_offset</code> || Vertical difference between referenced elevations or heads || metre (m) || <code>m</code> || <code>m</code> || Elevation, tank-bottom, and reservoir-head offsets
|-
| <code>link_diameter</code> || Internal or nominal diameter of a pipe or valve || millimetre (mm) || <code>mm</code> || <code>mm</code> || EPANET pipe and valve diameter
|-
| <code>tank_diameter</code> || Internal diameter of a cylindrical storage tank || metre (m) || <code>m</code> || <code>m</code> || EPANET tank diameter
|-
| <code>darcy_weisbach_roughness_height</code> || Absolute pipe-wall roughness height used by the Darcy-Weisbach formulation || millimetre (mm) || <code>mm</code> || <code>mm</code> || EPANET Darcy-Weisbach pipe roughness
|}
|}


=== Area and Volume ===
== Geographic Coordinate Quantities ==


{| class="wikitable"
{| class="wikitable"
! Quantity / Name !! Definition !! Canonical Unit (SI symbol) !! Serialized Unit !! EPANET Mapping
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
| <code>latitude</code> || Angular position north or south of the equator || degree (°) || <code>deg</code> || <code>deg</code> || WGS 84 latitude
|-
| <code>longitude</code> || Angular position east or west of the prime meridian || degree (°) || <code>deg</code> || <code>deg</code> || WGS 84 longitude
|-
|-
| area || Two-dimensional spatial extent || m² || m2 || Not directly used
| <code>projected_easting</code> || Eastward coordinate within a projected coordinate reference system || metre (m) || <code>m</code> || <code>m</code> || Projected-coordinate easting
|-
|-
| volume || Storage volume || m³ || m3 || Tank volume (SI-normalized EPANET model)
| <code>projected_northing</code> || Northward coordinate within a projected coordinate reference system || metre (m) || <code>m</code> || <code>m</code> || Projected-coordinate northing
|-
| <code>local_x</code> || X coordinate within an explicitly defined local engineering coordinate system || metre (m) || <code>m</code> || <code>m</code> || Local coordinates when the coordinate system is defined in metres
|-
| <code>local_y</code> || Y coordinate within an explicitly defined local engineering coordinate system || metre (m) || <code>m</code> || <code>m</code> || Local coordinates when the coordinate system is defined in metres
|}
|}


=== Flow and Transport ===
== Area and Volume Quantities ==


{| class="wikitable"
{| class="wikitable"
! Quantity / Name !! Definition !! Canonical Unit (SI symbol) !! Serialized Unit !! EPANET Mapping
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
|-
| volumetric_flow_rate || Volume per unit time || m³/s || m3_per_s || Link flow (SI-normalized EPANET model)
| <code>area</code> || Two-dimensional spatial extent || square metre (m²) || <code>m2</code> || <code>m2</code> || Tank cross-sectional area and other geometric areas
|-
|-
| mass_flow_rate || Mass per unit time || kg/s || kg_per_s || Not directly represented (derived)
| <code>volume</code> || Three-dimensional spatial extent or storage capacity || cubic metre (m³) || <code>m3</code> || <code>m3</code> || Tank volume
|}
|}


=== Pressure and Stress ===
== Flow and Transport Quantities ==


{| class="wikitable"
{| class="wikitable"
! Quantity / Name !! Definition !! Canonical Unit (SI symbol) !! Serialized Unit !! EPANET Mapping
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
|-
| pressure || Force per unit area in fluid system || Pa || pa || Node pressure (SI-normalized EPANET model)
| <code>volumetric_flow_rate</code> || Volume transported per unit time || cubic metre per hour (m³/h) || <code>m3/h</code> || <code>m3_per_h</code> || Demand, link flow, leakage flow, emitter flow, and pump-curve flow
|-
|-
| stress || Internal material stress || Pa || pa || Not represented
| <code>velocity</code> || Rate of linear movement || metre per second (m/s) || <code>m/s</code> || <code>m_per_s</code> || Link flow velocity
|}
|}


=== Time ===
== Hydraulic Head, Pressure, and Stress Quantities ==


{| class="wikitable"
{| class="wikitable"
! Quantity / Name !! Definition !! Canonical Unit (SI symbol) !! Serialized Unit !! EPANET Mapping
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
|-
| time || Simulation or observation time || s || s || Simulation time (EPANET internal time normalized to seconds)
| <code>hydraulic_head</code> || Total mechanical energy per unit weight of fluid expressed as an equivalent fluid-column height || metre (m) || <code>m</code> || <code>m</code> || Junction, reservoir, and tank hydraulic head
|-
|-
| duration || Time interval length || s || s || Simulation duration / reporting intervals
| <code>pressure_head</code> || Fluid pressure expressed as an equivalent fluid-column height || metre (m) || <code>m</code> || <code>m</code> || EPANET node pressure, pressure-driven demand thresholds, and pressure-control valve settings
|-
| <code>water_level</code> || Height of a water surface relative to a defined local reference level || metre (m) || <code>m</code> || <code>m</code> || Initial, minimum, maximum, and simulated tank levels
|-
| <code>head_gain</code> || Increase in hydraulic head across an energy-adding component || metre (m) || <code>m</code> || <code>m</code> || Pump curves and pump simulation results
|-
| <code>head_loss</code> || Reduction in hydraulic head across a hydraulic component || metre (m) || <code>m</code> || <code>m</code> || Pipes, valves, and other energy-dissipating components
|-
| <code>head_loss_gradient</code> || Hydraulic head loss per unit pipe length || metre per kilometre (m/km) || <code>m/km</code> || <code>m_per_km</code> || EPANET pipe head-loss reporting
|-
| <code>pressure</code> || Normal force per unit area within a fluid system || kilopascal (kPa) || <code>kPa</code> || <code>kpa</code> || Physical pressure measurements, sensors, SCADA data, and external exchange
|-
| <code>stress</code> || Internal force per unit area within a material || megapascal (MPa) || <code>MPa</code> || <code>mpa</code> || Structural and material analysis
|}
|}


=== Electrical Quantities ===
== Time Quantities ==


{| class="wikitable"
{| class="wikitable"
! Quantity / Name !! Definition !! Canonical Unit (SI symbol) !! Serialized Unit
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
|-
| current || Rate of electric charge flow || A || a
| <code>elapsed_time</code> || Time elapsed from a defined simulation or process origin || second (s) || <code>s</code> || <code>s</code> || Simulation elapsed time and time-based control triggers
|-
|-
| voltage || Electric potential difference || V || v
| <code>duration</code> || Length of a time interval || second (s) || <code>s</code> || <code>s</code> || Simulation duration and time steps
|-
|-
| resistance || Opposition to electric current flow || Ω || ohm
| <code>time_of_day</code> || Time elapsed since the start of the current day || second (s) || <code>s</code> || <code>s</code> || Simulation start time and clock-time controls
|}
 
== Hydraulic Coefficients and Other Dimensionless Quantities ==
 
The canonical UCUM unit identifier for all quantities in this section is <code>1</code>. The AOWIS unit suffix is omitted.
 
Semantic terms such as <code>ratio</code>, <code>factor</code>, <code>coefficient</code>, <code>multiplier</code>, and <code>exponent</code> describe the quantity and are not unit suffixes.
 
{| class="wikitable"
! Measurement Quantity Identifier !! Definition !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
|-
| power || Rate of energy transfer || W || w
| <code>hazen_williams_roughness_coefficient</code> || Hazen-Williams pipe roughness coefficient || <code>1</code> || none || EPANET Hazen-Williams roughness
|-
|-
| energy || Work or transferred electrical energy || J || j
| <code>chezy_manning_roughness_coefficient</code> || Chezy-Manning pipe roughness coefficient || <code>1</code> || none || EPANET Chezy-Manning roughness
|-
|-
| capacitance || Ability to store electric charge || F || f
| <code>minor_loss_coefficient</code> || Coefficient representing local hydraulic losses || <code>1</code> || none || Pipe and valve minor loss; TCV setting
|-
| <code>darcy_weisbach_friction_factor</code> || Darcy-Weisbach friction factor || <code>1</code> || none || Pipe simulation result
|-
| <code>pump_speed_ratio</code> || Pump rotational speed relative to nominal or reference speed || <code>1</code> || none || Pump setting, result, pattern, control, and rule values
|-
| <code>pattern_multiplier</code> || Factor applied by a hydraulic or energy pattern || <code>1</code> || none || EPANET pattern factor
|-
| <code>demand_multiplier</code> || Global factor applied to base demands || <code>1</code> || none || EPANET demand multiplier
|-
| <code>pressure_exponent</code> || Exponent used by the pressure-driven demand relation || <code>1</code> || none || EPANET pressure exponent
|-
| <code>emitter_exponent</code> || Exponent used by the emitter pressure-flow relation || <code>1</code> || none || EPANET emitter exponent
|-
| <code>reaction_order</code> || Order of a bulk, wall, or tank reaction equation || <code>1</code> || none || EPANET reaction order
|-
| <code>specific_gravity</code> || Fluid density relative to a defined reference density || <code>1</code> || none || EPANET specific gravity
|-
| <code>relative_viscosity</code> || Kinematic viscosity relative to the solver reference || <code>1</code> || none || EPANET relative viscosity
|-
| <code>relative_diffusivity</code> || Molecular diffusivity relative to the solver reference || <code>1</code> || none || EPANET relative diffusivity
|-
| <code>mixing_fraction</code> || Fraction of tank volume assigned to the applicable mixing zone || <code>1</code> || none || EPANET tank mixing fraction
|-
| <code>hydraulic_accuracy</code> || Relative hydraulic convergence criterion || <code>1</code> || none || EPANET hydraulic accuracy
|-
| <code>hydraulic_damping_limit</code> || Relative threshold controlling solver damping or status checks || <code>1</code> || none || EPANET damping limit
|-
| <code>relative_error</code> || Relative numerical error || <code>1</code> || none || Hydraulic simulation statistics
|-
| <code>flow_balance_ratio</code> || Ratio of total outflow to total inflow || <code>1</code> || none || EPANET flow-balance reporting
|-
| <code>quality_mass_balance_ratio</code> || Water-quality mass-conservation ratio || <code>1</code> || none || EPANET quality mass-balance reporting
|}
|}


== Data Representation Format ==
== Percentage Quantities ==


All AOWIS measurement values MUST use the following structure:
{| class="wikitable"
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
| <code>efficiency</code> || Ratio of useful output to total input expressed as a percentage || percent (%) || <code>%</code> || <code>percent</code> || Pump efficiency and efficiency curves
|-
| <code>relative_flow</code> || Flow relative to a defined reference flow || percent (%) || <code>%</code> || <code>percent</code> || Valve characteristic curves
|-
| <code>valve_position</code> || Valve opening position relative to its operating range || percent (%) || <code>%</code> || <code>percent</code> || Position-control valves
|-
| <code>source_trace_percentage</code> || Proportion of water originating from a specified source node || percent (%) || <code>%</code> || <code>percent</code> || EPANET source-trace analysis
|-
| <code>operating_time_percentage</code> || Fraction of a reporting period during which equipment operates || percent (%) || <code>%</code> || <code>percent</code> || Pump energy reporting
|-
| <code>demand_reduction_percentage</code> || Reduction in delivered demand relative to requested demand || percent (%) || <code>%</code> || <code>percent</code> || Hydraulic statistics
|-
| <code>leakage_loss_percentage</code> || Leakage loss relative to total system inflow || percent (%) || <code>%</code> || <code>percent</code> || Leakage statistics
|}
 
== Reaction and Leakage Quantities ==
 
{| class="wikitable"
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
| <code>first_order_bulk_reaction_coefficient</code> || First-order reaction-rate coefficient within the bulk fluid || per day (d⁻¹) || <code>/d</code> || <code>per_d</code> || Global, pipe, and tank first-order bulk reactions
|-
| <code>first_order_wall_reaction_coefficient</code> || First-order reaction-rate coefficient at a pipe wall || metre per day (m/d) || <code>m/d</code> || <code>m_per_d</code> || Global and pipe first-order wall reactions
|-
| <code>leak_area_per_100m_pipe_length</code> || Effective leak area assigned per 100 metres of pipe length || square millimetre per 100 metres (mm²/100 m) || <code>mm2/(100.m)</code> || <code>mm2_per_100m</code> || EPANET 2.3 FAVAD leak area; EPANET uses 100 project length units and the adapter converts when required<ref name="EPANET23">OWA-EPANET 2.3 release notes https://github.com/OpenWaterAnalytics/EPANET/blob/v2.3/ReleaseNotes2_3.md</ref>
|-
| <code>leak_area_expansion_per_pressure_head</code> || Increase in effective leak area per unit pressure head || square millimetre per metre of pressure head (mm²/m) || <code>mm2/m</code> || <code>mm2_per_m_head</code> || EPANET 2.3 FAVAD leak expansion
|}
 
== Water Quality Quantities ==
 
{| class="wikitable"
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
| <code>chemical_concentration</code> || Mass concentration of a chemical substance in water || milligram per litre (mg/L) || <code>mg/L</code> || <code>mg_per_l</code> || Chemical quality input and results
|-
| <code>chemical_mass_flow_rate</code> || Chemical mass introduced into or transported through the system per unit time || milligram per minute (mg/min) || <code>mg/min</code> || <code>mg_per_min</code> || EPANET mass-booster source strength and source mass rate
|-
| <code>water_age</code> || Time elapsed since water entered the modelled distribution system || hour (h) || <code>h</code> || <code>h</code> || EPANET water-age analysis
|}
 
== Power, Energy, and Electrical Quantities ==
 
{| class="wikitable"
! Measurement Quantity Identifier !! Definition !! Canonical Unit !! UCUM Identifier !! AOWIS Identifier Suffix !! AOWIS Model / EPANET Mapping
|-
| <code>power</code> || Rate of energy transfer || kilowatt (kW) || <code>kW</code> || <code>kw</code> || Pump power and electrical power
|-
| <code>energy</code> || Work performed or energy transferred || kilowatt-hour (kWh) || <code>kW.h</code> || <code>kw_h</code> || Pump energy consumption
|-
| <code>energy_intensity</code> || Energy consumed per unit volume || kilowatt-hour per cubic metre (kWh/m³) || <code>kW.h/m3</code> || <code>kw_h_per_m3</code> || Pump energy-use reporting
|-
| <code>electric_current</code> || Rate of electric charge flow || ampere (A) || <code>A</code> || <code>a</code> || Electrical model
|-
| <code>voltage</code> || Electric potential difference || volt (V) || <code>V</code> || <code>v</code> || Electrical model
|-
| <code>electrical_resistance</code> || Opposition to electric current flow || ohm (Ω) || <code>Ohm</code> || <code>ohm</code> || Electrical model
|-
| <code>capacitance</code> || Ability to store electric charge || farad (F) || <code>F</code> || <code>f</code> || Electrical model
|}
 
 
== Context-Dependent Quantity Resolution ==
 
Some Model concepts resolve to different registered measurement quantities depending on their context. The representation requirements for such values are defined in [[Measurement:Units]] and, where applicable, the corresponding Measurement subsystem specification.


<pre>
{| class="wikitable"
{
! Model Concept !! Resolved Measurement Quantity
  "quantity": "<physical_quantity>",
|-
  "value": <numeric_value>,
| Valve setting || PRV, PSV, and PBV: <code>pressure_head</code>; FCV: <code>volumetric_flow_rate</code>; TCV: <code>minor_loss_coefficient</code>; PCV: <code>valve_position</code>; GPV: curve reference rather than a measurement value
  "unit": "<canonical_unit>",
|-
  "uncertainty": <numeric_value>
| Pump setting || <code>pump_speed_ratio</code>
}
|-
</pre>
| Control trigger || <code>water_level</code>, <code>pressure_head</code>, <code>elapsed_time</code>, or <code>time_of_day</code>, depending on control type
|-
| Control or rule action setting || The measurement quantity supported by the target link type
|-
| Rule premise value || The measurement quantity selected by the rule variable
|-
| Initial or simulated quality || <code>chemical_concentration</code>, <code>water_age</code>, or <code>source_trace_percentage</code>, depending on quality-analysis mode
|-
| Quality-source strength || <code>chemical_concentration</code> or <code>chemical_mass_flow_rate</code>, depending on source type
|-
| Reaction coefficient || The applicable reaction-coefficient quantity determined by reaction order
|-
| Emitter coefficient || Equation-dependent coefficient in <code>Q = C H^n</code>; no single fixed canonical unit applies independently of <code>n</code>
|-
| Generic curve coordinate || The measurement quantity defined by the curve type
|-
| Report threshold || The measurement quantity of the corresponding report field
|-
| EPANET map or backdrop coordinate || The applicable geographic, projected, or local coordinate quantity after the coordinate representation is resolved
|}


Example:
== References ==


<pre>
<references />
{
  "quantity": "pipe_length",
  "value": 1200,
  "unit": "m",
  "uncertainty": 5
}
</pre>

Latest revision as of 11:12, 19 August 2026

This page is the normative registry of canonical measurement quantities and units used by AOWIS.

The representation and conversion rules governing these quantities are defined in Measurement:Units.

UCUM[1] is used for machine-readable physical unit identifiers.

Identifier and Field-Naming Rules

The canonical unit assigned to each measurement quantity in this registry is authoritative.

When a unit identifier is explicitly represented, it MUST use the canonical UCUM identifier defined here.

The AOWIS identifier suffix is an ASCII-safe naming convention used for fixed-schema field names, property names, database columns, and similar technical identifiers.

The suffix convention is:

  • division is represented by _per_;
  • multiplication is represented by _;
  • unit symbols are normalized to lower case where required for identifier naming;
  • quantity-specific semantic qualifiers MAY be included where a literal unit-only suffix would be ambiguous;
  • dimensionless fields with canonical UCUM unit 1 normally omit a unit suffix.

For example: 

m3/h        -> m3_per_h
m/s         -> m_per_s
kW.h/m3     -> kw_h_per_m3
mm2/(100.m) -> mm2_per_100m

The AOWIS identifier suffix is not itself a UCUM unit identifier.

For generic or dynamically typed measurement values, the resolved measurement quantity determines the canonical unit through this registry.

Length and Distance Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
length Linear spatial extent along an object or path metre (m) m m Pipe and link length
elevation Vertical height relative to an engineering or hydraulic datum metre (m) m m Junction, tank, reservoir, and terrain elevation
altitude Vertical position reported by a geographic positioning source metre (m) m m Geographic altitude; not necessarily suitable as hydraulic elevation
distance Spatial separation between positions metre (m) m m Derived geometric distance
vertical_offset Vertical difference between referenced elevations or heads metre (m) m m Elevation, tank-bottom, and reservoir-head offsets
link_diameter Internal or nominal diameter of a pipe or valve millimetre (mm) mm mm EPANET pipe and valve diameter
tank_diameter Internal diameter of a cylindrical storage tank metre (m) m m EPANET tank diameter
darcy_weisbach_roughness_height Absolute pipe-wall roughness height used by the Darcy-Weisbach formulation millimetre (mm) mm mm EPANET Darcy-Weisbach pipe roughness

Geographic Coordinate Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
latitude Angular position north or south of the equator degree (°) deg deg WGS 84 latitude
longitude Angular position east or west of the prime meridian degree (°) deg deg WGS 84 longitude
projected_easting Eastward coordinate within a projected coordinate reference system metre (m) m m Projected-coordinate easting
projected_northing Northward coordinate within a projected coordinate reference system metre (m) m m Projected-coordinate northing
local_x X coordinate within an explicitly defined local engineering coordinate system metre (m) m m Local coordinates when the coordinate system is defined in metres
local_y Y coordinate within an explicitly defined local engineering coordinate system metre (m) m m Local coordinates when the coordinate system is defined in metres

Area and Volume Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
area Two-dimensional spatial extent square metre (m²) m2 m2 Tank cross-sectional area and other geometric areas
volume Three-dimensional spatial extent or storage capacity cubic metre (m³) m3 m3 Tank volume

Flow and Transport Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
volumetric_flow_rate Volume transported per unit time cubic metre per hour (m³/h) m3/h m3_per_h Demand, link flow, leakage flow, emitter flow, and pump-curve flow
velocity Rate of linear movement metre per second (m/s) m/s m_per_s Link flow velocity

Hydraulic Head, Pressure, and Stress Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
hydraulic_head Total mechanical energy per unit weight of fluid expressed as an equivalent fluid-column height metre (m) m m Junction, reservoir, and tank hydraulic head
pressure_head Fluid pressure expressed as an equivalent fluid-column height metre (m) m m EPANET node pressure, pressure-driven demand thresholds, and pressure-control valve settings
water_level Height of a water surface relative to a defined local reference level metre (m) m m Initial, minimum, maximum, and simulated tank levels
head_gain Increase in hydraulic head across an energy-adding component metre (m) m m Pump curves and pump simulation results
head_loss Reduction in hydraulic head across a hydraulic component metre (m) m m Pipes, valves, and other energy-dissipating components
head_loss_gradient Hydraulic head loss per unit pipe length metre per kilometre (m/km) m/km m_per_km EPANET pipe head-loss reporting
pressure Normal force per unit area within a fluid system kilopascal (kPa) kPa kpa Physical pressure measurements, sensors, SCADA data, and external exchange
stress Internal force per unit area within a material megapascal (MPa) MPa mpa Structural and material analysis

Time Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
elapsed_time Time elapsed from a defined simulation or process origin second (s) s s Simulation elapsed time and time-based control triggers
duration Length of a time interval second (s) s s Simulation duration and time steps
time_of_day Time elapsed since the start of the current day second (s) s s Simulation start time and clock-time controls

Hydraulic Coefficients and Other Dimensionless Quantities

The canonical UCUM unit identifier for all quantities in this section is 1. The AOWIS unit suffix is omitted.

Semantic terms such as ratio, factor, coefficient, multiplier, and exponent describe the quantity and are not unit suffixes.

Measurement Quantity Identifier Definition UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
hazen_williams_roughness_coefficient Hazen-Williams pipe roughness coefficient 1 none EPANET Hazen-Williams roughness
chezy_manning_roughness_coefficient Chezy-Manning pipe roughness coefficient 1 none EPANET Chezy-Manning roughness
minor_loss_coefficient Coefficient representing local hydraulic losses 1 none Pipe and valve minor loss; TCV setting
darcy_weisbach_friction_factor Darcy-Weisbach friction factor 1 none Pipe simulation result
pump_speed_ratio Pump rotational speed relative to nominal or reference speed 1 none Pump setting, result, pattern, control, and rule values
pattern_multiplier Factor applied by a hydraulic or energy pattern 1 none EPANET pattern factor
demand_multiplier Global factor applied to base demands 1 none EPANET demand multiplier
pressure_exponent Exponent used by the pressure-driven demand relation 1 none EPANET pressure exponent
emitter_exponent Exponent used by the emitter pressure-flow relation 1 none EPANET emitter exponent
reaction_order Order of a bulk, wall, or tank reaction equation 1 none EPANET reaction order
specific_gravity Fluid density relative to a defined reference density 1 none EPANET specific gravity
relative_viscosity Kinematic viscosity relative to the solver reference 1 none EPANET relative viscosity
relative_diffusivity Molecular diffusivity relative to the solver reference 1 none EPANET relative diffusivity
mixing_fraction Fraction of tank volume assigned to the applicable mixing zone 1 none EPANET tank mixing fraction
hydraulic_accuracy Relative hydraulic convergence criterion 1 none EPANET hydraulic accuracy
hydraulic_damping_limit Relative threshold controlling solver damping or status checks 1 none EPANET damping limit
relative_error Relative numerical error 1 none Hydraulic simulation statistics
flow_balance_ratio Ratio of total outflow to total inflow 1 none EPANET flow-balance reporting
quality_mass_balance_ratio Water-quality mass-conservation ratio 1 none EPANET quality mass-balance reporting

Percentage Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
efficiency Ratio of useful output to total input expressed as a percentage percent (%) % percent Pump efficiency and efficiency curves
relative_flow Flow relative to a defined reference flow percent (%) % percent Valve characteristic curves
valve_position Valve opening position relative to its operating range percent (%) % percent Position-control valves
source_trace_percentage Proportion of water originating from a specified source node percent (%) % percent EPANET source-trace analysis
operating_time_percentage Fraction of a reporting period during which equipment operates percent (%) % percent Pump energy reporting
demand_reduction_percentage Reduction in delivered demand relative to requested demand percent (%) % percent Hydraulic statistics
leakage_loss_percentage Leakage loss relative to total system inflow percent (%) % percent Leakage statistics

Reaction and Leakage Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
first_order_bulk_reaction_coefficient First-order reaction-rate coefficient within the bulk fluid per day (d⁻¹) /d per_d Global, pipe, and tank first-order bulk reactions
first_order_wall_reaction_coefficient First-order reaction-rate coefficient at a pipe wall metre per day (m/d) m/d m_per_d Global and pipe first-order wall reactions
leak_area_per_100m_pipe_length Effective leak area assigned per 100 metres of pipe length square millimetre per 100 metres (mm²/100 m) mm2/(100.m) mm2_per_100m EPANET 2.3 FAVAD leak area; EPANET uses 100 project length units and the adapter converts when required[2]
leak_area_expansion_per_pressure_head Increase in effective leak area per unit pressure head square millimetre per metre of pressure head (mm²/m) mm2/m mm2_per_m_head EPANET 2.3 FAVAD leak expansion

Water Quality Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
chemical_concentration Mass concentration of a chemical substance in water milligram per litre (mg/L) mg/L mg_per_l Chemical quality input and results
chemical_mass_flow_rate Chemical mass introduced into or transported through the system per unit time milligram per minute (mg/min) mg/min mg_per_min EPANET mass-booster source strength and source mass rate
water_age Time elapsed since water entered the modelled distribution system hour (h) h h EPANET water-age analysis

Power, Energy, and Electrical Quantities

Measurement Quantity Identifier Definition Canonical Unit UCUM Identifier AOWIS Identifier Suffix AOWIS Model / EPANET Mapping
power Rate of energy transfer kilowatt (kW) kW kw Pump power and electrical power
energy Work performed or energy transferred kilowatt-hour (kWh) kW.h kw_h Pump energy consumption
energy_intensity Energy consumed per unit volume kilowatt-hour per cubic metre (kWh/m³) kW.h/m3 kw_h_per_m3 Pump energy-use reporting
electric_current Rate of electric charge flow ampere (A) A a Electrical model
voltage Electric potential difference volt (V) V v Electrical model
electrical_resistance Opposition to electric current flow ohm (Ω) Ohm ohm Electrical model
capacitance Ability to store electric charge farad (F) F f Electrical model


Context-Dependent Quantity Resolution

Some Model concepts resolve to different registered measurement quantities depending on their context. The representation requirements for such values are defined in Measurement:Units and, where applicable, the corresponding Measurement subsystem specification.

Model Concept Resolved Measurement Quantity
Valve setting PRV, PSV, and PBV: pressure_head; FCV: volumetric_flow_rate; TCV: minor_loss_coefficient; PCV: valve_position; GPV: curve reference rather than a measurement value
Pump setting pump_speed_ratio
Control trigger water_level, pressure_head, elapsed_time, or time_of_day, depending on control type
Control or rule action setting The measurement quantity supported by the target link type
Rule premise value The measurement quantity selected by the rule variable
Initial or simulated quality chemical_concentration, water_age, or source_trace_percentage, depending on quality-analysis mode
Quality-source strength chemical_concentration or chemical_mass_flow_rate, depending on source type
Reaction coefficient The applicable reaction-coefficient quantity determined by reaction order
Emitter coefficient Equation-dependent coefficient in Q = C H^n; no single fixed canonical unit applies independently of n
Generic curve coordinate The measurement quantity defined by the curve type
Report threshold The measurement quantity of the corresponding report field
EPANET map or backdrop coordinate The applicable geographic, projected, or local coordinate quantity after the coordinate representation is resolved

References

  1. ↑ Unified Code for Units of Measure (UCUM) https://ucum.org
  2. ↑ OWA-EPANET 2.3 release notes https://github.com/OpenWaterAnalytics/EPANET/blob/v2.3/ReleaseNotes2_3.md
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