Water used in the GWRS is first treated at the Orange County Sanitation District (OCSD). OCSD collects more than 200 million gallons (757,000 cubic meters) of wastewater per day and removes a high degree of impurities through several processes. A stringent source control program limits metals and chemicals flowing into OCSD's plants in Fountain Valley and Huntington Beach. The wastewater undergoes treatment through bar screens, grit chambers, trickling filters, activated sludge, clarifiers and disinfection processes before it is sent to the GWRS. It is vital that the water meet stringent water quality standards before it enters the GWRS.