The Thirst Response
Ideally, we would all be able to rely on our body’s mechanism of thirst to determine when we should be consuming more water, either through drinking water or consuming food that contains water. The thirst mechanism, in theory, should not only provide our body with enough information to know when to drink water, but also on how much water to drink based on intensity of the thirst mechanism. The issue with relying solely on this thirst sensation arises from an inability for us to adequately assess the thirst response in some cases. Firstly, studies demonstrate that as we age, our thirst response is blunted. Older individuals typically do not drink enough fluids to replenish water loss when compared to younger individuals (1). The mechanism for this is not well explained, but could be due to a loss of sensation to thirst from a lifetime of failing to respond to the body’s alarm system for water. In essence, the longer we ignore our body's plea for water or mistake it for hunger, the perception of thirst can be altered and result in a weaker thirst signal (2).
Your Water Intake Recommendation
What I am going to recommend to you is starting with a baseline recommendation for water intake and modifying based on individual factors such as diet, thirst, caffeine intake and sweat time which I’ll go through below.