Nitrate pollution in water—invisible to the naked eye yet harmful to human health and ecosystems—is a growing concern in both agricultural and urban areas. The Aquality App, developed by Deltares, empowers farmers, water authorities, and even citizen scientists to track nitrate, salinity, and nutrient levels in surface water, groundwater, and drainage systems. It helps users identify pollution hotspots, evaluate the effectiveness of mitigation measures, and contribute to a shared database for better water management. The app also supports DIY testing for mineral nitrogen (Nmin), ammonium, and phosphate, making it a versatile tool for professionals and community-driven water quality projects alike.