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 [14].

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 [22].

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

Flow

  • 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

  • 0.001 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