It has only a single waterlock and so there is no retention of the water in it when a period of draughts like the ones this summer happen.
Germany has had a project for adding water locks to the Rhine ongoing in burocracy purgatory for the last 26 years now, and if this situation doesn't shake things up I don't think anything ever will.
There is still enough water, it is just unevenly distributed over the year. Previously winter snow was retained in the Alps and released as it melted during the summer, nowadays winter rain immediately comes downstream as giant floods.
If upstream countries were able to retain a significant portion of those floods and release it as a trickle during the summer, The Netherlands wouldn't have any problems. It is literally impossible for it to be worse than it currently is.
Besides, most of the water used in The Netherlands does not come from the large rivers, but from local rainfall. The drought is due to sticking to the historical policy of trying to immediately get rid of any excess water, rather than retaining it locally. No need to do anything EU-wide to solve that, just get the farmers to accept that the land will be a bit soggy in the winter.
It's going to be a huge future fight in the EU because all countries upstream will want to retain 'all' the water and the remaining low flow will still have all those countries their industries dumping toxic waste, meaning the ratio of water-waste will get ridiculous.