Students need to understand fecal coliform bacteria. This is bacteria that comes from mammal waste and can be an indicator of a sewage spill, or something else that contaminates the water (like a feedlot upstream).
Sometimes, I am short the funds to buy fecal coliform tests (which cost between $70-$100) for all my students. This year, I decided to spend my funds elsewhere and filmed the process instead. Students filled in a section of their Water Quality Virtual Lab using this video.
Students took data and determined water quality based on the results. Its not as good as kids getting the hands-on experience, but can do in a pinch if funds are needed elsewhere or if time is crunched.
I also do Biological Oxygen Demand via video due to the lack of surface water near my school.