If you are thirsty, that’s your body telling you that you have left it really late to drink. It’s a delicate balance between rushing to the bathroom all the time and not drinking enough. Your body NEEDS water to survive and being dehydrated, even a little, will significantly reduce your physical capabilities.
You will need to find the right amount of water for YOUR situation, but start today with at least 1.5 litres and adjust accordingly. It’s such a simple topic but with a little effort can bring a real difference in your performance. I have a sports drink bottle that I fill 4 times a day. I use that because it makes it easy to know how much I have drunk.
One last thing, it IS possible to drink too much but you would need to be drinking over 5 litres per day for that to happen, but that doesn’t mean you should be drinking 4 litres per day either! Just be sensible.