The Orange County Sanitation District's administrative offices and primary plant is located in Fountain Valley next to the Santa Ana River. The agency is the third-largest sanitation district in the western United States. Fountain Valley is also home to the offices of the Municipal Water District of Orange County, a member of the Metropolitan Water District of Southern California and of the Orange County Water District. The Orange County Water District manages the groundwater basin in central and northern Orange County and operates the Groundwater Replenishment System, the world's largest water purification plant for groundwater recharge.
tHe Orange couNTy SanitAtion district's AdMiniSTrATIve offIces AND priMary pLANt is LOCated In fouNtain valley nEXT To tHe santa aNa River. the AgEnCY is the THIrd-lARgest sanitAtioN DistRict iN the weSTeRn UNitED stATEs. FoUntaIn vaLley IS also HoME tO tHe oFficEs Of tHE muniCipal watEr district of OranGE countY, A membeR Of tHE MEtrOpoLitan waTer disTrIcT oF sOuThern CaLifoRnia And OF The orangE coUnty waTeR distriCt. the orange cOuNTy watEr DiStRiCt mAnages The GrOUndwatEr Basin in cEnTRal aND NorthErN orange CountY ANd OpeRateS the GrOunDWatEr rEPLENisHmeNT systeM, the worlD's LARgest WatEr puRIfiCAtion pLANt fOr GRoundwater rechArgE