I am glad to hear that you are training outside and not just in the gym. Generally speaking you should consume about a litre of water per hour of arduous physical exercise. If the enviroment that you are training in is warm or hot then you will need to look at increasing the amount of water you are drinking. Though the heat of the sun in this country isnt really sufficient to bring temperatures that require increased amounts of hydration above a litre, even when exercising in Iraq in the heat out there the body only needs about 1.5 litres per hour of exercise, providing that you are well hydrated throughout the day. A good rule is pee clear twice a day and you are hydrated.
If you like training outdoors why not train with me and supercharge your fitness the Army way for ultimate fitness you can ring me on 07814683245 or visit http://www.dosctraining.co.uk
, all the best Dan.