http://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_Hydro/
"MERIT Hydro is a global hydrography datasets, developed based on the MERIT DEM and multiple inland water maps. It contains flow direction, flow accumulation, hydrologically adjusted elevations, and river channel width."
Requires registration but provides better data for waterways.
For elevation data I use Merit-DEM :
https://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_DEM/
cheers