In this episode, I discuss our body’s most vital and essential nutrient—water. I explain the structure of water and how it is used by the cells and tissues of our body, how much water we each need to drink and when in order to optimize our mental focus and physical performance; and I include how exercise, humidity, heat, and caffeine affect our hydration needs. I explain how temperature and pH influence water’s physical properties and if there is any scientific basis for drinking so-called “pH water” or “alkalized water” to improve health. I explain how to test your tap water for contaminants (e.g., endocrine disruptors) and the documented problems with fluoride in drinking water. I provide options for filtering drinking water and describe different water types (e.g., reverse osmosis, hydrogen-enriched, electrolyzed reduced, deuterium depleted, etc.). Since the human body is mostly water (55-80% depending on one’s age) and water has essential roles in health, disease and cellular function, everyone ought to benefit from understanding how best to clean our tap water, hydrate effectively and in some cases, adjust the type of water we drink to allow our brain and body to function optimally in regard to health and performance.