The USGS Water Science School
All of the information on the Water Science School site is in the "public domain." In other words, it is owned by the Nation's citizens. Feel free to use any of the information, data, and pictures -- you don't have to ask for permission.
Oftentimes, when you use material from another source, you need to "reference" the source. If you want to reference material from this Web site, here's how.
For example, if you want to reference the information from the page titled "Acid Rain":
U.S. Geological Survey. "Acid Rain." Water Science School World Wide Web site. (April 21, 2016). [Online] Avaiable at https://water.usgs.gov/edu/acidrain.html [Accessed on July 4, 2016].
Note: The "(April 21, 2016)" is the date of last revision to the Web page (found at the bottom of all of our pages), and the "[Accessed on July 4, 2016]" is the date that you accessed the Web site.