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Introduction

Hydra is a water infrastructure simulation platform written in Rust. It is built as a suite of domain engines sharing one toolchain: a desktop GUI, a hydra CLI, and a Rust SDK.

EngineDomainSource modelStatus
Water Distribution (wds)Pressurised supply networks — hydraulics, water quality, energyEPANET .inp (2.x)Available
Urban Drainage (uds)Stormwater and wastewater collection — runoff, routing, qualitySWMM .inpPlanned
Open Channel (och)Rivers and channels — steady and unsteady flowHEC-RAS projectPlanned

See Engines for what each engine covers and what “planned” means in practice.

Water Distribution Engine

The engine that ships today. It performs extended-period simulation (EPS) of hydraulic behaviour and water quality dynamics across pressurised pipe networks, computing the full time history of flows, pressures, and constituent concentrations at every node and link.

Unless a page says otherwise, the rest of this documentation describes this engine.

Hydraulics

  • Head-loss formulas: Hazen-Williams, Darcy-Weisbach, Chezy-Manning (with minor losses)
  • Demand models: Demand-Driven Analysis (DDA) and Pressure-Dependent Analysis (PDA)
  • Emitters: pressure-dependent outflow at junctions
  • Leakage: FAVAD (Fixed and Variable Area Discharge) model
  • Pumps: head-curve (1/3-point and custom), constant-power, variable-speed patterns
  • Valves: PRV, PSV, FCV, TCV, GPV, PBV, PCV
  • Tanks: cylindrical and volume-curve geometries, overflow mode
  • Controls: simple time/level/pressure controls, rule-based controls with priorities
  • Solver: Global Gradient Algorithm (GGA) with sparse Cholesky factorisation

Water Quality

  • Modes: chemical constituent, water age, source trace
  • Transport: Lagrangian segment-based advection
  • Reactions: first-order and zero-order bulk and wall decay, limiting potential, roughness correlation
  • Sources: concentration, mass booster, flow-paced booster, setpoint booster
  • Tank mixing: complete (CSTR), two-compartment, FIFO (plug flow), LIFO

I/O

  • Input: EPANET .inp format, any 2.x release (local files, HTTP URLs)
  • Output: EPANET-compatible .out binary format, .rpt text report, .json report
  • Unit systems: all 11 EPANET flow unit variants (CFS, GPM, MGD, IMGD, AFD, LPS, LPM, MLD, CMH, CMD, CMS)

Relationship to EPANET

The water distribution engine’s hydraulic and quality solvers were derived by studying EPANET’s mathematical foundations. Hydra is not an EPANET clone or compatibility layer; it is a distinct solver that models the same physics. Where the two diverge, Hydra’s result is authoritative.

The same principle will apply to each engine Hydra adds: it reads the established source-model format for its domain, and models the physics independently rather than reimplementing the reference tool.

For migration guidance, see Migrating from EPANET.

See INP Format Support for current EPANET input coverage.