Rud Ab District () is in Narmashir County, Kerman province, Iran. Its capital is the city of Nezamshahr.
After the 2006 National Census, Narmashir and Rud Ab Districts were separated from Bam County in the establishment of Narmashir County, which was divided into two districts of two rural districts each, with Narmashir as its capital.
At the time of the 2006 National Census, the district's population (as a part of Bam County) was 13,816 in 3,452 households. The following census in 2011 counted 14,079 people in 3,843 households, by which the district had been separated from the county in the establishment of Narmashir County. The 2016 census measured the population of the district as 14,138 inhabitants in 4,277 households.