I was always told to drink more than usual, after i suffered the concussion. The minimum should be 2 litres daily. But where is the limit? Normally I'm drinking an average of 3 litres. Is that a good value?

There should be a chart or formula somewhere - it is related to what your body weight is.. So a larger person would be able to drink more water than a smaller person..

[“It depends on your size and weight, and also on your activity level and where you live,” Nessler says. “In general, you should try to drink between half an ounce and an ounce of water for each pound you weigh, every day.” For example, if you weigh 150 pounds, that would be 75 to 150 ounces of water a day. If you’re living in a hot climate and exercising a lot, you’d be on the higher end of that range; if you’re in a cooler climate and mostly sedentary, you’d need less.]
http://www.webmd.com/diet/water-for-...ss-diet?page=2

[Hydration Calculator

Water is essential for your good health, but you might need more water than you think. I designed this hydration calculator to help you decide how much water you need. Answer all the questions based on how you feel and what your activity levels are today:]
http://nutrition.about.com/library/b...calculator.htm