Calculation of floor area for canal/water costs

We have received the costs for sewer/water from the municipality. That is okay. What makes me somewhat suspicious is the calculation of the underlying floor area. As far as I have informed myself, the floor area is determined based on the exterior dimensions of the building on all full stories. And full stories are above-ground stories if they have a height of at least 2.30 m over at least three quarters of their floor area. However, in our case, the basement was fully calculated as a full story, as was the upper floor, which has more than a quarter of sloping ceilings.

Does it make sense to complain about this, or is there another decision stating that all available stories may be used as the basis of calculation with their full floor square meters?

It would of course make a big difference in terms of price!

We have received a cost calculation for the participation in the costs for the new wastewater treatment plant. The calculation also included all floors with the floor area, including the basement and slope. I asked myself the same question.