Final answer:
Drinking pure water is essential to health because it provides hydration and improves brain function.
Step-by-step explanation:
Drinking pure water is essential to health because it provides hydration by replenishing the water continuously lost from the body through urine, sweat, and exhaling. This helps regulate body temperature, aids in digestion and circulation, and flushes out bacteria and viruses. Additionally, water improves brain function, as the brain is composed of 85% water and requires proper hydration to function optimally.