Nigeria is a signatory to the United Nations Sustainable Development Goals (SDGs). Target 6.2 of Goal 6 has requested countries who are parties to the SDGs to end open defecation by 2030. Notwithstanding this, the Government of Nigeria launched a far more ambitious National Road Map in 2016 to end open defecation in the country by 2025. Since water and sanitation are inextricably linked, this paper estimates Nigeria's freshwater requirement to attain open-defecation-free status by 2025. The analysis revealed that the quantity of freshwater required amounted to between 2.74 and 2.94 × 106 cubic metres (m3) per day or between 1.0 and 1.1 × 109 m3 per year under the assumptions made. This amount is relatively less than Nigeria's total water resources potential estimated at 375.1 × 109 m3/year. The data presented will help increase the reliability of estimates of water for sanitation in Nigeria.