Drinking water doesn't "clean" you, it stops your kidneys from failing altogether.
You should always pound down water after heavy drinking. It's the only physiological cure for hangovers.
So I disagree.
A good way to test it - do it yourself. You will see a noticeable difference. Go in the evening after the gym. Hydrate yourself through the day and you will see a huge difference in performance.
There is quite a lot of talk about it in sports/gym circles for many years.
This is demonstrably untrue, and trvial to prove to oneself. A more significant contributor is GABA adaptation and up-regulation by the CNS.
I'm not downplaying dehydration as a factor, but to say it's the ONLY thing is ridiculous.
There has been a lot of talk about it for years in many sport/gym related communities. Those people know how to observe their bodies and reaction.
https://www.reuters.com/article/us-india-liquor/deaths-mount...
The worse you feel the next day after alcohol means the more significant damage you did to your body. If you feel fresh, it says that the damage was almost non-existent (besides liver, which, if you drink a lot of alcohol you should take care separately). Then drinking a lot of water before going to bed will help your body to clean from alcohol.
It's all about alcohol-drinking culture. In some countries drinking alcohol 2-4 times a week is normal (as long as you don't drink to get wasted). But I have seen places (for example Ireland), where drinking to get wasted is an ultimate goal 2-4 times a week. That's the problem imo. Better education and public awareness would help a lot.