Contamination of drinking water with toxic arsenic affects more than 170 million people worldwide. Because arsenic is tasteless, colorless, and odorless when mixed with water, almost all people consume it unknowingly and suffer from health impairments (like skin-related diseases or cancer). Running a randomized controlled trial with 2,334 Indian households, we show that providing inexpensive information how to reduce exposure to arsenic contamination in drinking water has significant effects even one year after the intervention. First, it generates knowledge about arsenic’s harmful effects. Second, it improves drinking water treatment practices. Third, treated households are between 2.7 and 9.3 percentage points more likely to consume safe drinking water. We also find suggestive evidence for improvements with respect to stomach-related health issues. With costs of less than 2 Euros per disability-adjusted life year averted our intervention is very cost-effective.