"We never know the value of water until the well is dry." The individuals in this audience are involved in all aspects of water treatment, including inspecting sewage, collecting sewage, testing water samples, and purifying water. They have been seen researching companies such as Enviro-Care, or Jenfitch in addition to content related to the commercial, industrial, and governmental treatment of water.
Mass and energy are the two key components of the knowable universe, and individuals in this audience represent the industries attempting to sell the latter to public and private individuals and corporations. They may have been observed inspecting buildings for air leakage, advising customers and companies on efficient energy practices, and installing devices like solar panels or gas meters.
Waste treatment represents the attempt of governmental and private organizations to minimize, convert, and reuse refuse. They may be researching waste treatment applications for ammonia or chlorine, specifics of recording and gauge readings for waste treatment, or companies like Rumpke or Recology.