Obviously, it's very bad to contaminate drinking water through mining. However,

“The health effects of long-term, low-level lithium exposure remain uncertain,” according to senior author Kathrin Schilling, PhD, MSc, assistant professor of Environmental Health Sciences at Columbia Mailman School of Public Health. “While lithium has been used safely for decades as a medication to treat bipolar disorder at doses far higher than environmental exposure levels, less is known about the potential health implications of chronic exposure through drinking water.”

There are numerous studies that show other benefits of higher lithium levels in the blood as well. Mining runoff would be my last choice for a source, of course.