There are lot of confusion about water, how much, when and what type of water to drink ayurveda has all the answers of these questions. 

Q. When and how much water we should drink? 

There is a very simple answer to this. In healthy condition when you feel thirsty you should then only drink water and amount of water also according to thirst. Thirst is a natural urge when body requires water it gives single and we have to just full fill the need of body. Internet is flooded with information like drink more and more water to stay hydrated or to remove toxins but when you put anything in body without its requirement its only going to harm it same goes with water, so just follow the instruction of your body instead of listening to unverified source. Thirst depends on weather, physical activity, age and type of food you eat so it is a very individual thing, we cannot generalize it. This is the beauty of Ayurveda, it never gives one fix rule for all as we all are different body type. 

Q. Cold or warm water which one to prefer?

Cold water is not recommended by Ayurveda, in summer water from earthen pot is advised otherwise normal room temperature water in normal weather and warm water in cold climate is recommended.