hydration is not just about getting water in, it is about getting fluid that your body can actually use. tap water in a lot of places comes with chlorine, fluoride, microplastics, trace heavy metals, and PFAS. none of that helps hydration. it just adds extra stuff your kidneys have to filter and it does nothing for electrolytes. plain water also dilutes sodium and potassium if you drink a lot of it fast, which is why people feel bloated or light-headed after chugging it. your cells need potassiu

Introduction to Pressure & Fluids - Physics Practice Problems