Free Online Water Distribution Network Calculator with the EPANET Solver

Notes

Steady state

Solves one set of demands at a time, using the same global gradient algorithm EPANET uses. It does not model how the network changes over time. A tank is held at the water level you give it: within one solution it never runs down and never fills.

Not modeled

Water quality and demands that change through the day are not modeled. Valves are: 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.

Planned additions

Scenarios, so that one project can hold several sets of demands. Tables of node and pipe results. Writing EPANET .inp files, so that a project can go back out to EPANET. Comments and suggestions are always welcome (see the feedback link above).

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.