When modeling water quality, pressures, per se, are not the best indicator of calibration. The best calibration would be against water quality measurements. Absent that, the most important variable to calibrate against is flow. Of course, flow measurements in a distribution system are a real luxury, so we need to use pressure data as advantageously as possible.

It seems to me that setting a simple tolerance (i.e. plus or minus x psi) is not the best way to calibrate a water quality model. What you really want to represent realistically is the shape of the grade surface.

We also need to consider the precision of pressure measurements themselves. Remember the old saying: measure with micrometer, mark with chalk, cut with axe.

I'm looking forward to what others have to say on this subject.

Regards,
Ben Harding
blh@hydrosphere.com