The Toolkit uses an unformatted binary output file to store both hydraulic and water quality results at uniform reporting intervals. Data written to the file is either 4-byte integers, 4-byte floats, or fixed-size strings whose size is a multiple of 4 bytes. This allows the file to be divided conveniently into 4-byte records. The file consists of four sections of the following sizes in bytes:
| Section | Size in Bytes |
| Prolog | 884 + 36*Nnodes + 52*Nlinks + 8*Ntanks |
| Energy Usage | 28*Npumps + 4 |
| Dynamic Results | (16*Nnodes + 32*Nlinks)*Nperiods |
| Epilog | 28 |
where:
- Nnodes = number of nodes (junctions + reservoirs + tanks),
- Nlinks = number of links (pipes + pumps + valves),
- Ntanks = number of tanks and reservoirs,
- Npumps = number of pumps,
- Nperiods = number of reporting periods.
All of these counts are themselves written to the file's Prolog or Epilog sections.
Prolog Section
The Prolog section of an EPANET binary output file contains the following data:
| Item | Type | # Bytes |
| Magic Number = 516114521 | Integer | 4 |
| Version (= 200) | Integer | 4 |
| Number of Nodes | Integer | 4 |
| Number of Reservoirs & Tanks | Integer | 4 |
| Number of Links | Integer | 4 |
| Number of Pumps | Integer | 4 |
| Number of Valves | Integer | 4 |
| Water Quality Option - see EN_QualityType | Integer | 4 |
| Traced Node Index | Integer | 4 |
| Flow Units Option | Integer | 4 |
| Pressure Units Option | Integer | 4 |
| 0 = psi | |
| 1 = meters | |
| 2 = kPa | |
| Report Statistic Type - see EN_StatisticType | Integer | 4 |
| Reporting Start Time (sec) | Integer | 4 |
| Reporting Time Step (sec) | Integer | 4 |
| Simulation Duration (sec) | Integer | 4 |
| Project Title (1st line) | Char | 80 |
| Project Title (2nd line) | Char | 80 |
| Project Title (3rd line) | Char | 80 |
| Name of Input File | Char | 260 |
| Name of Report File | Char | 260 |
| Name of Quality Chemical | Char | 32 |
| Chemical Concentration Units | Char | 32 |
| ID String of Each Node | Char | 32*Nnodes |
| ID String of Each Link | Char | 32*Nlinks |
| Index of Head Node of Each Link | Integer | 4*Nlinks |
| Index of Tail Node of Each Link | Integer | 4*Nlinks |
| Type Code of Each Link (see EN_LinkType) | Integer | 4*Nlinks |
| Node Index of Each Tank | Integer | 4*Ntanks |
| Surface Area of Each Tank | Float | 4*Ntanks |
| Elevation of Each Node | Float | 4*Nnodes |
| Length of Each Link | Float | 4*Nlinks |
| Diameter of Each Link | Float | 4*Nlinks |
Energy Usage Section
The Energy Usage section of an EPANET binary output file contains the following data:
| Item (Repeated for Each Pump) | Type | # Bytes |
| Pump Index in list of links | Integer | 4 |
| Pump Utilization (%) | Float | 4 |
| Average Efficiency (%) | Float | 4 |
| Average kwatts/MGal (or kwatts/cu m) | Float | 4 |
| Average kwatts | Float | 4 |
| Peak kwatts | Float | 4 |
| Average Cost per Day | Float | 4 |
| Peak Energy Usage (kw-hrs) | Float | 4 |
Dynamic Results Section
The Dynamic Results section of an EPANET binary output file contains the following set of data for each reporting period (the reporting time step is written to the Output File's
Prolog Section and the number of such steps is written to the
Epilog Section):
| Item | Type | # Bytes |
| Demand at Each Node | Float | 4*Nnodes |
| Head (Grade) at Each Node | Float | 4*Nnodes |
| Pressure at Each Node | Float | 4*Nnodes |
| Water Quality at Each Node | Float | 4*Nnodes |
| Flow in Each Link | Float | 4*Nlinks |
| (negative for reverse flow) | |
| Velocity in Each Link | Float | 4*Nlinks |
| Headloss per 1000 Units of Length for Each Link | Float | 4*Nlinks |
| (total head for pumps and head loss for valves) | |
| Average Water Quality in Each Link | Float | 4*Nlinks |
| Status Code for Each Link | Float | 4*Nlinks |
| 0 = closed (pump shutoff head exceeded) | |
| 1 = temporarily closed | |
| 2 = closed | |
| 3 = open | |
| 4 = active (partially open | |
| 5 = open (pump max. flow exceeded) | |
| 6 = open (FCV can't supply flow | |
| 7 = open (PRV/PSV can't supply pressure) | |
| Setting for Each Link | Float | 4*Nlinks |
| Reaction Rate for Each Link (mass/L/day) | Float | 4*Nlinks |
| Friction Factor for Each Link | Float | 4*Nlinks |
Epilog Section
The Epilog section of an EPANET binary output file contains the following data:
| Item | Type | # Bytes |
| Average bulk reaction rate (mass/hr) | Float | 4 |
| Average wall reaction rate (mass/hr) | Float | 4 |
| Average tank reaction rate (mass/hr) | Float | 4 |
| Average source inflow rate (mass/hr) | Float | 4 |
| Number of Reporting Periods | Integer | 4 |
| Warning Flag: | Integer | 4 |
| 0 = no warnings | |
| 1 = warnings were generated | |
| Magic Number = 516114521 | Integer | 4 |
