Many government agencies collect and publish statistics. The easiest way to find these statistics are by using the 'site' search on Google.
This search will bring up only government websites. This can be a great way not only to find the information you're looking for, but also to find out what government agencies are collecting this data. For instance, the search above brings up a lot of results from both the United States Geological Survey (USGS) and the Environmental Protection Agency (EPA).
Below are some examples of encyclopedias and dictionaries for water related topics.
How to Find Reference Resources
Some reference sources that can help for this course: