Units¶
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].
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 