The District’s on-site laboratory is certified by the California State Water Resources Control Board’s Environmental Laboratory Accreditation Program (ELAP) and is part of the Environmental Services Division. The laboratory staff perform routine sampling of the District’s wastewater treatment plant processes and conduct testing of recycled water and wastewater for the purpose of plant process monitoring and National Pollutant Discharge Elimination System (NPDES) permit compliance. The laboratory provides high-quality analytical results for recycled water and wastewater and reports data to various regulatory agencies. More than 600 tests are run each month by the lab staff, seven days a week, 365 days a year.

GSD's laboratory is certified in three fields of testing: microbiology of drinking water (for recyled water monitoring), microbiology of wastewater, and inorganic chemistry of wastewater. To maintain accreditation, the analysts participate in proficiency testing sample analyses annually. The following list is the specific testing for which the lab holds certification:

• Total Coliforms (Drinking Water - SM 9223 B)
• Total and Fecal Coliforms (Wastewater – SM 9221 B, C, E)
• Enterococci (Wastewater - Enterolert)
• Total Oil and Grease (Wastewater – EPA 1664)
• Turbidity (Wastewater – SM 2130 B)
• Filterable Residue, TDS (Wastewater – SM 2540 C)
• Nonfilterable Residue, TSS (Wastewater – SM 2540 D)
• Settleable Residue (Wastewater – SM 2540 F)
• Total Residual Chlorine (Wastewater – SM 4500-CL, G)
• Hydrogen Ion, pH (Wastewater – SM 4500-H + B)
• Biochemical Oxygen Demand (Wastewater – SM 5210 B)

The laboratory is staffed 365 days a year by a team compsoed of three full-time employees: two analysts and the Environmental Services Manager. In addition, the Safety and Regulatory Coordinator is also part of the Environmental Services team. Operations staff occasionally assist in the laboratory to provide shift coverage. Laboratory staff are certified laboratory analysts through the California Water Environment Association (CWEA) Technical Certification Program.