Pywr

Pywr simulates water-resource networks — reservoirs, transfers, demands, environmental flows — by solving an allocation problem (linear programme) at every timestep. Models are defined in JSON or Python, run very fast, and integrate cleanly with pandas and the scientific Python stack, which makes Pywr well suited to Monte Carlo yield studies, climate-scenario screening and optimisation-in-the-loop work.

Developed at the University of Manchester and used in national-scale water resource planning (including England's regional water resources programme), it is one of the most credible open alternatives to commercial system-simulation packages like WEAP or Aquator.