Source: USGS
In this USGS Landsat in Action video, Martha Anderson, with the U.S. Department of Agriculture, talks about the value of Landsat and its thermal data for understanding agricultural lands.
Quote to note:
“With Landsat we can see temperature of individual fields and how it varies from field-to-field. The temperature of the land surface gives us a good indication of how rapidly water is evaporating off that surface. And this is really important for knowing how healthy the crops are and also for supplying information for irrigators: how much water was used last week and how much do they need to replenish in the current week to keep the crops healthy.”

Above the Earth, Below the Surface: Landsat’s Role in Monitoring Water Quality
Safeguarding freshwater resources is crucial, and while scientists use a variety of ground-based techniques to gauge water quality, the Landsat program has provided water quality data from orbit for decades.