Units#
All data in WNTR is stored in the following SI (International System) units:
Acceleration = \(\rm g\) (\(\rm g \equiv 9.80665 m/s^2\))
Concentration = \(\rm kg/m^3\)
Demand = \(\rm m^3/s\)
Diameter = \(\rm m\)
Elevation = \(\rm m\)
Energy = \(\rm J\)
Flow rate = \(\rm m^3/s\)
Head = \(\rm m\)
Headloss = \(\rm m\)
Length = \(\rm m\)
Mass = \(\rm kg\)
Mass injection = \(\rm kg/s\)
Power = \(\rm W\)
Pressure head = \(\rm m\) (assumes a fluid density of 1000 \(\rm kg/m^3\))
Time = \(\rm s\)
Velocity = \(\rm m/s\)
Volume = \(\rm m^3\)
When setting up analysis in WNTR, all input values should be specified in SI units. All simulation results are also stored in SI units and can be converted to other units if desired, for instance by using the SymPy Python package [13].
EPANET unit conventions#
WNTR can generate water network models from EPANET INP files using all EPANET unit conventions. When using an EPANET INP file to generate a water network model, WNTR converts model parameters to SI units using the Units and Quality options of the EPANET INP file. These options define the mass and flow units used in the file. Some units also depend on the equation used for pipe roughness headloss and on the reaction order specified.
For reference, Table 4 includes EPANET unit conventions [21].
Parameter 
US customary units 
SIbased units 

Concentration 
mass /L where mass can be defined as mg or ug 
mass /L where mass can be defined as mg or ug 
Demand 
Same as flow 
Same as flow 
Diameter (Pipes) 
in 
mm 
Diameter (Tanks) 
ft 
m 
Efficiency (Pumps) 
percent 
percent 
Elevation 
ft 
m 
Emitter coefficient 
flow / sqrt(psi) 
flow / sqrt(m) 
Energy 
kWhours 
kWhours 
Flow 


Friction factor 
unitless 
unitless 
Hydraulic head 
ft 
m 
Length 
ft 
m 
Minor loss coefficient 
unitless 
unitless 
Power 
horsepower 
kW 
Pressure 
psi 
m 
Reaction coefficient (Bulk) 
1/day (1storder) 
1/day (1storder) 
Reaction coefficient (Wall) 


Roughness coefficient 


Source mass injection rate 
mass /min 
mass /min 
Velocity 
ft/s 
m/s 
Volume 
ft ^{3} 
m ^{3} 
Water age 
hours 
hours 