Our brains depend on proper hydration to function optimally. Brain cells require a delicate balance between water and various elements to operate, and when you lose too much water, that balance is disrupted. Your brain cells lose efficiency.
Water is also needed for the brain’s production of hormones and neurotransmitters. Nerve transmission requires one-half of all the brain’s energy.
The average adult brain is 1.3 to 1.4kg and is approx 2% (obviously varies) of the overall weight of the adult human. The brain is 70-80% water and at least two more significant fluids which are reliant upon the availability of water indirectly are present: blood @ 150 ml (10%) and cerebrospinal fluid (CSF) @ 150 ml (10%)