Debating How Much Weed Killer Is Safe in Your Water Glass. nytimes. August 22, 2009 .For decades, farmers, lawn care workers and professional green thumbs have relied on the popular weed killer atrazine to protect their crops, golf courses and manicured lawns. But atrazine often washes into water supplies and has become among the most common contaminants in American reservoirs and other sources of drinking water. Now, new research suggests that atrazine may be dangerous at lower concentrations than previously thought. Recent studies suggest that, even at concentrations meeting current federal standards, the chemical may be associated with birth defects, low birth weights and menstrual problems. [ See ]