National Agencies:
USGS EPA DOE USBR
USGS Groundwater Page
USGS, National Water Quality Assessment Program
USGS, Groundwater Modeling Software
USGS, Manual for the Collection of Water Quality Data
USGS, Groundwater Atlas for the U.S.
USGS, Interactive Educational Material on Water and Groundwater
USGS, Techniques for Water Resources Investigations
USGS, National Field Manual for Collection of Water Quality Data
EPA, Office for Groundwater & Drinking Water
EPA, Center for Subsurface Modeling Support
EPA, Software for Environmental Awareness
EPA, USDA: Proposed Guidelines, Animal Feeding Operations
EPA, USDA: Joint Statement on TMDL related Ag Issues, 5/2000
EPA, Atlas of America's Polluted Waters
EPA Ag Center
International Hydrological Programme (UNESCO): Publications
U.S. Salinity Laboratory Modeling Support
USDA-NRCS Technical References (Soils Handbook, etc.)
USDA-NRCS Animal Waste Management
The National Academies' Water Information Center

National Professional Organizations:
American Geophysical Union (AGU) - Hydrology Section
National Ground Water Association (NGWA)
American Water Resources Association (AWRA)

News and Outreach:
US Water News
Water Tech Online
Groundwater Foundation
Volunteer Monitor, National Newsletter of Volunteer Water Quality Monitoring
American Groundwater Trust
National Ground Water Research and Education Foundation (NGWERF)

Other Interesting Groundwater Sites:
 Groundwater Modeling Resources
Vadose Zone Modeling Resources
Well Owner Information, Education, and Resources (through NGWA)
Hydrology Related Web Sites (through AGU)
The Hydrologic Cycle - A Basic Introduction
Nitrate and the "Blue Baby Syndrome" (WSU Agrichemical and Environmental News)
Nitrate in groundwater FAQ; (Santa Clara Valley Water District)
WSU Pesticide Information Center On-Line
Toxicological Profiles of Hazardous Substances (ATSDR)
EPA's Groundwater Primer on the Web
Water-related Pseudo-Science - Links and Information
Ken Bannister's Groundwater Page
Richard Winston's Groundwater Modeling Page
Interactive Groundwater Flow and Transport Models (Univ. of Illinois)
Smith-Comesky Ground Water Science
The Hydrogeologist's Homepage
Soil Water Monitoring and Measurement Booklet
A Ready Reference for Irrigation, Manual of Practice
Assessing the TMDL Approach to Water Quality Mgmt (Nat. Research Council Report)
NGWA 2002 McEllhiney Lecturer: John H. Schnieders (Well Rehabilitation)
University of California, Davis, Groundwater Modeling Weblinks

Resources for Educators:
The Educator Toolbox (Watersheds, Water Quality; Stormwatercoalition.org)
Ploppy: Groundwater Webpage for Children (in Spanish)

Christmas 2004 Indian Ocean Tsunami disaster - groundwater impacts:
UK Groundwater Forum
International Groundwater Resources Assessment Center