How much do I need to drink to stay hydrated and avoid fainting? This common question is discussed here. How much water you will need to help you stop fainting or feeling faint will vary between people. It will also depend on where you are and what you are doing.
People who faint need to work keep their ‘fluid tank close to full’. If you have no other medical condition for which your doctor has specifically asked you to limit your fluid intake, you should aim for a minimum of 2 L or non-caffeinated fluids a day. However, at times you may need more.
We lose half a litre of water each day just from breathing. So imagine if it is very hot and you are sweating more or have has a stomach upset then you will have to make up for the extra fluids you have lost.
We recommend that you have majority of your fluid intake earlier on in the day, aiming for at least a total of 2L by mid afternoon and then taper off towards the end of the day. This is because you are probably more active earlier on in the day and will require a good volume in your system to keep you going. On the days that you participate in physical activities or exercises, you need to make sure you drink at least 0.5L of fluid even before starting exercise and continue to consume fluid throughout the work out.
Remember all non caffeinated and non alcoholic fluids count not just plain water.