The claim that "you can drink too much water" is true. There's multiple credible resources that confirm this claim and explain the negative health consequences that come with over hydration. According to a blog post by University Hospitals (a nationally ranked healthcare system based in Cleveland, OH), they claim that excessive hydration can "overwhelm your kidneys" and lead to a condition called hyponatremia. Symptoms of hyponatremia include headache, fatigue, confusion, and distinct muscle cramping and weakness. Overall, there's several credible sources that confirm this claim, and they're 100% true.