In the sweltering heat of a summer afternoon, few things are more rewarding than a cold glass of water. The first sip might even elicit an exaggerated sigh of relief. Why does something as simple as drinking water immediately feel so refreshing?

          Headshot of Yuki Oka.
Yuki Oka, a biologist at the California Institute of Technology, studies how the brain controls behaviors toward homeostatic regulation, particularly fluid regulation, by balancing water and minerals.
California Institute of Technology

Our bodies are wired to seek ways to fulfill basic needs, like quenching thirst, and come with an internal reward system when we maintain fluid balance. Thirst neurons in the brain signal to our bodies with an unmistakable cue: a parched, scratchy sensation in the back of the throat.1,2 The first gulp of water feels euphoric because the brain responds with a rush of dopamine, a feel-good neurotransmitter, even though it takes 15 to 30 minutes for water to dilute the bloodstream.

“The concept of satiation or rehydration and the rewarding feeling are separable components,” explained Yuki Oka, a biologist at the California Institute of Technology. The body knows when thirst is truly satiated based on multiple sensory pathway signals. 

Oka’s group identified two types of thirst satiation neurons. One activates after gulping water and releases dopamine, while the other responds to the gut monitoring changes in water concentration.3 Activating both neuron types is necessary to fully quench thirst and feel like a liquid reward.4 When Oka’s team bypassed the signals induced by gulping and administered water directly to the gut, dopamine wasn’t released.

Now, with each sip of cool, refreshing water, imagine a mini celebration between the body and the brain in a toast to staying hydrated.

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  1. Zimmerman CA, et al. Nature. 2016;537(7622):680-684. 
  2. Martins PR, et al. Rev Esc Enferm USP. 2017;51:e03240.
  3. Augustine V, et al. Nature. 2018;555:204-209.
  4. Augustine V, et al. Neuron. 2019;103(2):242-249.e4.