• California Groundwater Association – www.groundh2o.org

• San Bernardino Environmental Health Services – www.sbcounty.gov/dehs

• Department of Water Resources – www.dwr.water.ca.gov

• National Groundwater Association – www.ngwa.org

• U S Water Filters – www.filterpros.com

• U S Filter and Pentek Filters – www.waterfiltersonline.com