If you have a reference to a document published by a U. S. government agency, first check Worldcat Discovery. Searching by the publication title is the quickest way to search. A large number government documents are now available online and either Worldcat Discovery or the Library Catalog will include a link to the publication.
Should you find call numbers beginning with the prefix Doc Dept, these documents will generally be in print located on the South end of the 4th floor.
There may be government documents available online but not showing up in the Library Catalog. Search for a title using a site search in Google or consider a keyword search specifying ".gov" sites as follows: idaho water supply site:.gov, bringing up information from a variety of government agencies.