A complete nitrogen mass balance for all wastewater generated in the Central Arizona–Phoenix ecosystem was developed using data from the 18 largest wastewater treatment plants (99% of flow). Components included total N in raw wastewater, denitrification in wastewater treatment plants, biosolids production, and effluent (reuse, recharge, and discharge). Denitrification and biosolids production remove 81% of wastewater N. Nearly all biosolids are recycled to cotton fields within the ecosystem. Most effluent is recycled within the ecosystem. As the result of wastewater management practices developed to reuse wastewater, wastewater N is either deliberately volatilized or accumulates within the system; only 4% of the original wastewater N is exported via the Gila River.