Here's a wheel from my own back yard. It was distributed by the Edwards Aquifer Authority a few years ago. From top to bottom, this measures 8.75 inches. The disk is 6.75 inches.
It's kind of a fun way to communicate how to conserve water. I did not know you shouldn't use the toilet as a trash can! I wonder if Heloise knows that? I'd better tell her!
According to Wikipedia:
The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water supply for agriculture and industry in the aquifer’s region. In addition, the Edwards Aquifer feeds the Comal and San Marcos springs, provides springflow for recreational and downstream uses in the Nueces, San Antonio, Guadalupe, and San Marcos river basins, and is home to several unique and endangered species.