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| <code>capacitance</code> || Ability to store electric charge || farad (F) || <code>F</code> || <code>f</code> || Electrical model
| <code>capacitance</code> || Ability to store electric charge || farad (F) || <code>F</code> || <code>f</code> || Electrical model
|}
|}
== Context-Dependent Measurement Values ==
The following concepts cannot be assigned one fixed canonical unit until their applicable context has been resolved.
{| class="wikitable"
! Model Concept !! Context-Dependent Meaning !! Required Representation
|-
| Valve setting || PRV, PSV, and PBV: pressure head; FCV: volumetric flow rate; TCV: minor-loss coefficient; PCV: valve position; GPV: curve reference || Use quantity-specific fields or a discriminated valve-setting structure
|-
| Pump setting || Pump speed relative to nominal speed || Resolve as <code>pump_speed_ratio</code>
|-
| Control action setting || Quantity supported by the controlled link type || Use the same quantity-specific setting representation as the target link
|-
| Control trigger || Water level, pressure head, elapsed time, or time of day depending on control type || Use quantity-specific trigger representations
|-
| Rule premise value || Quantity selected by the rule variable || Store or resolve the rule variable together with its quantity-specific value
|-
| Rule action setting || Quantity supported by the target link || Use the target link's quantity-specific setting representation
|-
| Initial and simulated quality || Chemical concentration, water age, or source-trace percentage depending on analysis mode || Resolve through the active quality-analysis mode
|-
| Water-quality solver tolerance || Quantity depends on quality-analysis mode || Resolve through the active quality-analysis mode
|-
| Quality-source strength || Chemical concentration or chemical mass flow rate depending on source type || Use a source-type-specific representation
|-
| Reaction coefficient || Dimensions depend on reaction order || Use fixed quantities only for defined fixed-order cases; otherwise retain the reaction order with the coefficient
|-
| Emitter coefficient || In <code>Q = C H^n</code>, the dimensional meaning of <code>C</code> depends on <code>n</code> || Store coefficient and exponent together
|-
| Generic curve coordinates || Quantities depend on curve type || Prefer typed curve structures; genuinely generic curves require explicit quantity metadata
|-
| Report thresholds || Quantity depends on the corresponding report field || Associate each threshold with the report field's measurement quantity
|-
| EPANET map and backdrop coordinates || Coordinate interpretation depends on the associated map configuration || Resolve to an explicitly identified geographic, projected, or local coordinate representation
|}
== Monetary Values ==
Monetary values that depend on a currency MUST identify that currency using its ISO 4217 alphabetic code or by reference to a configured currency carrying that code.<ref name="ISO4217">ISO 4217 currency codes https://www.iso.org/iso-4217-currency-codes.html</ref>
Where a monetary value is normalized by a physical quantity, the physical quantity uses the canonical unit defined by this registry.
For example:
{| class="wikitable"
! Concept !! Physical Denominator
|-
| Energy price || kilowatt-hour (kWh)
|-
| Demand charge || kilowatt (kW)
|-
| Daily cost rate || day (d)
|}
== AOWIS Model and Backend Mapping ==
Fixed-schema Model fields encode their canonical unit through the schema and, where applicable, the AOWIS identifier suffix.
Backend-selected unit systems MUST NOT alter those field semantics.
The EPANET adapter converts backend values whenever the EPANET project representation differs from the canonical AOWIS representation. Relevant mappings include:
* volumetric flow rate → <code>m3/h</code>;
* length and hydraulic head → <code>m</code>;
* link diameter → <code>mm</code>;
* tank diameter → <code>m</code>;
* Darcy-Weisbach roughness → <code>mm</code>;
* head-loss gradient → <code>m/km</code>;
* leakage area → <code>mm2/(100.m)</code>;
* leakage expansion → <code>mm2/m</code> of pressure head;
* energy intensity → <code>kW.h/m3</code>;
* chemical concentration → <code>mg/L</code>;
* chemical mass flow rate → <code>mg/min</code>.


== References ==
== References ==


<references />
<references />

Revision as of 17:19, 18 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.

Generic or dynamically typed measurement values MUST identify their resolved measurement quantity and use the canonical unit defined by 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

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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