How accurate must the elevation data be? The answer depends on the accuracy desired in pressure calculations vs. the amount of labor and cost allotted for data collection. For example, the HGL calculated by the model is significantly more precise than any of the elevation data. Since 2.31 ft.of elevation translates into 1 psi of pressure (for water), calculating pressure to 1 psi precision requires elevation data that is accurate to roughly 2 ft. Elevation data that is accurate to the nearest 10 ft. will result in pressure that is accurate to roughly 4 psi.

The lack of precision in elevation data (and pressure results) also leads to questions regarding water distribution design. If design criteria state that pressure must exceed 20 psi and the model gives a pressure of 21 (+/- 4) psi or 19 (+/-4) psi, the engineer relying on the model will have to decide if this design is acceptable.