Answering the question, "Is a model calibrated?" is a lot like answering the question, "Did you stop beating your dog?" There is no yes and no, black and white answer. There are just varying shades of gray.

Adequacy of model calibration depends on the cumulative effects of errors, approximations, assumptions and projections and necessarily falls on a spectrum somewhere between a perfect model (that doesn't exist) and a perfectly incorrect model. All models lie somewhere in that spectrum and the adequacy of calibration depends on the circumstances and the intended use.

There are so many applications of models that I have my doubts about the possibility of developing standards. The real test is whether you can use the model to support you decision making.

I disagree with Ben and Krister's comments that water quality data are needed for model calibration. About 98% of model applications deal with fire flow and pipe sizing and water quality isn't explicitly considered. This points out the fact that different people have different ideas about what a model should do. (Remember the old story about the blind men and the elephant.)

Best wishes,
Tom Walski
Pennsylvania American Water Company