One way to teach students about water quality and/or how scientists go about their work is to share articles with them. Here is a great article entitled "Study Maps Hidden Water Pollution in U.S. Coastal Areas". This research shows a great example of the use of both NASA satellite data and ground-based data. In this study, the researchers used U.S. topographic data as well as NASA climate models to "identify key inland regions that contribute groundwater and contaminants to the coast. They examined rainfall, evaporation rates and the amount of known surface runoff to calculate the missing portion of water that was running out below ground, then melded those results with terrain and land-use data to identify where the water ended up. The team was able to learn more about the previously hidden water exchanges via computer analyses, without extensive and costly field surveys." They also discuss the impact of agriculture, urbanization, climate change, and topography on water quality, and explored both the issues with the mixing of salt and freshwater as well as ocean water contamination.
This article includes picture and graphs, and would be a fabulous way to show students the importance of looking at multiple data sets to determine the quality of water and to determine how various areas are impacted and can impact water quality.