All data in WNTR is stored in the following SI (International System) units:

  • Length = \(m\)
  • Diameter = \(m\)
  • Water pressure = \(m\) (this assumes a fluid density of 1000 \(kg/m^3\))
  • Elevation = \(m\)
  • Mass = \(kg\)
  • Time = \(s\)
  • Concentration = \(kg/m^3\)
  • Demand = \(m^3/s\)
  • Velocity = \(m/s\)
  • Acceleration = \(g\) (1 \(g\) = 9.81 \(m/s^2\))
  • Energy = \(J\)
  • Power = \(W\)
  • Mass injection = \(kg/s\)
  • Volume = \(m^3\)

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. The SymPy Python package can be used to convert between units [JCMG11].

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 using the units defined in the Units and Quality options of the EPANET INP file. These options define the mass and flow units for the model. 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 [Ross00].

Table 4 EPANET INP File Unit Conventions
Parameter US customary units SI-based 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 kW-hours kW-hours
  • CFS: ft 3 /s
  • GPM: gal/min
  • MGD: million gal/day
  • IMGD: million imperial gal/day
  • AFD: acre-feet/day
  • LPS: L/s
  • LPM: L/min
  • MLD: million L/day
  • CMH: m 3 /hr
  • CMD: m 3 /day
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 (1st-order) 1/day (1st-order)
Reaction coefficient (Wall)
  • mass /ft/day (0-order)
  • ft/day (1st-order)
  • mass /m/day (0-order)
  • m/day (1st-order)
Roughness coefficient
  • 10 -3 ft (Darcy-Weisbach)
  • unitless (otherwise)
  • mm (Darcy-Weisbach)
  • unitless (otherwise)
Source mass injection rate mass /min mass /min
Velocity ft/s m/s
Volume ft 3 m 3
Water age hours hours