The high cost of equipment to monitor water quality often puts valuable health tools out of reach for many communities in developing countries. Our low-cost device measures the turbidity, or "cloudiness", of water due to suspended particles, and can detect potentially dangerous concentrations of dirt in water -- even when they are invisible to the human eye! Our device integrates with a remote data-acquisition system to enable record keeping and real-time observation of water quality in rivers, wells, and treatment plants.