Is notification for water supply allowed according to the newer regulations?

In our area, every house built in recent decades has, of course, paid its water connection fee normally. However, the municipality has now noticed that enormous costs arise from the renovation of the sewer system, which are then simply passed on to the citizens via an "improvement contribution." In plain terms, this means about 1000€ per house as a contribution to the municipality.

Something like this or similar could happen in your case. You initially pay according to the old statute, but then you get another bill for the difference

Oh wow. That sounds really arbitrary. In our purchase contract for the property, it says regarding water supply: "The amounts are final. Additional claims or refunds are excluded."

In our purchase agreement for the property, it says regarding the water supply: "The amounts are final. Additional claims or refunds are excluded."