In reply toby Wouter Groeneveld
You might try the European INSPIRE portal to see if there’s any water data there that covers la Wallonie. It wouldn’t be the first time that data which isn’t available locally is provided to a supranational entity that then does publish it. Although mostly the INSPIRE portal doesn’t have current measurement data, just the locations of the measurement stations.
For Flanders, public rainfall and water level data is accessible through waterinfo.be. The water bomb hit Wallonia the hardest though, and that data is of course not available on waterinfo.be. Another reason to unify our already too divided country…