Many roads tagged residential when it seems they aren't.

Waterways not linked with the dams

Voir osm.org/changeset/43639585#map=19/43.28594/5.52376

check if the waterway really exist and stop here. (suspicious import)

check waterway direction

Complete waterway and fix direction in the town center.
Elevation data (use OpenCycleMap render to see it) shows that all waterways should converge to the town. But then where is the water going?

lakes might be linked

check if the waterway really exist and stop here. (suspicious import)

check if stream still there and if it really ends without going to the river

Check if the steams are there and if they really stop there