Free Online Water Distribution Network Calculator with the EPANET Solver

Notes

How it is solved

Each moment is solved with the same global gradient algorithm EPANET uses. Set a total run time and the EPANET solver calculates every reporting step in turn: tanks fill and drain, demands follow their patterns, and the toolbar plays the run back. The built-in solver calculates one moment at a time and holds every tank at its starting level.

Not modeled

Water quality is not modeled. Valves: a throttle valve works in either solver, and the valves that open and close on their own (PRV, PSV, FCV) are solved with the EPANET solver, which this page turns on by itself when your network holds one.

Saving projects

Every project is a tab, and every tab is saved in this browser as you work. Clearing your browser data deletes them all, so keep your work in a file: File, Save as. An asterisk on a tab means it holds changes that are not in a file. Nothing is ever written to a file unless you ask. In some browsers a project connects to the file you save it to, and File, Save writes back to that same file from then on; in others no connection is possible, so Save is disabled and only Save as is available. When a project file is kept on a shared drive, this page tells you if a colleague already has it open, so that two people do not write over each other.

Pump curve

A pump follows H = H₀ − aQ^b, where H is the head the pump adds and Q is the flow through it. Enter one, two, or three points from the manufacturer's curve. Three points — the head at zero flow, the normal working point, and the point of highest flow — fit H₀, a and b directly, and follow a published curve most closely. Two points fit a parabola (b = 2) with its peak at zero flow. One point uses a common rule: the head at zero flow is 1.33 × the head you enter, and the highest flow is 2 × the flow you enter, which again gives b = 2. A pump with no points entered adds no head at all. The curve is not cut off where the head reaches zero, so asking a pump for more flow than its curve can deliver gives a negative head. The fix is a bigger pump or a smaller demand, not a different curve fit.

Also on this page

A project can sit on real ground with a street map behind it. EPANET .inp files can be read in and written out. The bottom panel draws a profile along a route and lists the junctions. Assets can be colored by their results, and Find picks out every asset that meets a test.

Color band boundaries stay the same

Color band boundaries are set when you choose a data classification method. They are not set again at each time step, because that would make the colors mean something new at every step, and that is not helpful for visualizing your system. EPANET works the same way. To get new boundaries, choose a method again or type your own.

Hazen-Williams constants match EPANET

In August 2026 the Hazen-Williams coefficient and exponent were changed to match EPANET. Head loss results differ from earlier versions of this page by up to 0.1 percent, which is far smaller than the uncertainty in the C value itself.

Which EPANET this page runs

The EPANET solver on this page is OWA-EPANET 2.3.5, released on 20 February 2025. EPANET is developed by Open Water Analytics, a community that works with the United States Environmental Protection Agency, which released version 2.2.0 in December 2019. The run report calls it 2.3.05 because the engine writes the last number in two digits. It reaches this page through epanet-js 0.9.0 by Luke Butler, under the MIT licence, and it runs inside your browser: your network is never sent anywhere to be solved.