It might not be the same for everyone. However, I have noticed that I rarely drink water. It is interesting that I only noticed that this year (late twenties). The effects on my body and mind were phenomenal. I used to drink less than 1 liter a day.
I don't feel thirst. So I don't drink water when I'm dehydrated (because I almost never feel it). Instead, I have a prescribed quantity that I drink everyday. Also when I'm out for food/coffee/bar I always order a bottle of water. I might not drink all of it, but it'll help me drink.
You should drink 3-4 liters per day to feel the difference. The difference will be massive only if you are dehydrate it without realizing it. In my case, I was severely dehydrated, but I never noticed it.
The effects: I feel fresher. Smarter. More active. My eyes are much less sore and I suffer less when I'm looking at a screen. It is interesting I have never noticed or thought that water dehydration was the cause. The first days that I started the water dosing, I felt that the exhaustion was relieved.
To give you an idea of how serious this is. Look at this chart: https://i.pinimg.com/originals/3e/ed/4a/3eed4ad01533479b473e... My pee color was always on the extreme side before. I have never questioned it. Talk about ignorance.
The very first days of hydration, I felt almost 10 years younger. By continuing I certainly no longer feel the effects since I'm used to the new standards. But I'll never forget the day I discovered that I was in severe dehydration. I also will not forget the almost instantaneous change in my body after the few hours of drinking.