Hydration during long rides

How much hydration is enough hydration during long rides?

That guide should be helpful: https://cyklopedia.cc/cycling-tips/hydration-for-cycling/

Whenever you feel thirsty feel free to take some water As long as you arent filling your stomach enough that you cant ride.

If you feel thirsty it is a little too late, it is a first sign that you are dehydrated, you should drink around every 15 min, a small amount of water.