Initial Publication Date: September 24, 2025

The Freshwater pcMEL

The Freshwater pcMEL asks students to weigh the connections between evidence and alternative explanations about the quantity and quality of freshwater resources. The availability of usable freshwater as the world's population grows is a critical environmental issue facing Earth and its inhabitants.

The Models

Model A: Earth's freshwater challenges will be solved by engineering solutions.
Model B: Earth has a shortage of freshwater, which will worsen as our world's population increases.

Student Handouts


Lines of Evidence

Evidence #1: Land use changes have generated large pressures on freshwater resources. These changes are affecting both water quality and availability.
Evidence #2: The world's population is increasing. This stresses the supply of freshwater.
Evidence #3: Water reclamation and desalination are expensive. The costs vary depending on location.
Evidence #4: Advances in engineering have led to better access to quality drinking water. At the same time life expectancy and quality of life have improved.


Student Handouts

Virtual MEL

*NOTE: The virtual materials below are from an older version of the activity than what is posted above.

The Google Drive folder below contains MEL resource documents in the Google formats. In order to maximize the flexibility of our activities, the MEL Project Team wanted to make more resources compatible with virtual settings. We have made our MEL scaffolds available in Google formats, so that they can be copied, modified, and uploaded more easily on a variety of platforms and devices. Please note that to access all the materials for each MEL scaffold, you will need a Google account. View the README file first.