I presume you are referring to drinking whilst riding, if so its supposed to be about a litre an hour. I cannot remember the correct figure but its only about a 2% loss in body fluids and its around a 3% reduction in muscular endurance time. I do a lot of 100+ mile rides solo and only carry 2 x 750ml bottles of drink. Because I am solo, it becomes hard to find somewhere to replenish my supplies, as I do not carry a big lock, I need to find a safe shop where I know my bike will still be outside when I come out of the shop. And if I cannot, then I have to keep going, but the drink is always planned out to last me the full ride for such an enventuallity and not consumed in the first 50 miles, I need fluid to last till at least the last 5 miles, so drink has to be rationed.
The effects it has on me if I do not replen is, I start to tire around the 70 mile mark and when I get to the 90's, headaches start to set in and hallucinations sometimes. When I am lucky and can buy an additional litre of water, I am OK till I get to 90 miles before I start suffering. On long ride's I always weigh myself before and after to see what my weight loss is, and it is always around 5lb - 6lb, which oddly enough equates to around a 2%- 3% loss in fluids, my bodyweight being around 213lb. Therefore as water weighs 10lb a gallon, I have lost the equivalent of 4pts of fluid. On getting home, I will try to replace all that fluid as soon as I can, my first pint of water will always contain at least half a gramme to a gramme of salt. Despite drinking about 4 pints of water and weeing clear afterwards for the rest of the day and night, a day later I can see that I am still dehydrated as my wee will be dark orange again, so I still have to drink more than what I lost on the ride.
But at the end of the day a lot depends on how far you are riding and how hard, and the actual temperature you are riding in, plus what you wear, too much clothes and you'll overheat, thus more perspiration.
Once you have done a few rides, and took some weight measurements, you soon know what your envelope for cycling is, go out of it and then you have to start planning your rides.