The area administered by the office starts from Nanzhuang and Dahu townships in Miaoli County to the west of the Central Mountain Range; to Houlong and Zhunan Townships facing the Taiwan Strait in the west, south from Sanyi Township, north to Emei and Beipu townships in Hsinchu County and some districts of Hsinchu City; The areas includes three counties (cities) and 17 townships and districts: Miaoli City, Houlong, Zhunan, Toufen, Gongguan, Zaoqiao, Touwu, Sanyi, Tongluo, Xihu, Dahu, Sanwan, Nanzhuang in Miaoli County; Emei, Beipu and Baoshan Townships in Hsinchu County, and Hsinchu City.
The water sources of irrigation systems administered by the office include Houlong River, Xihu River, Zhonggang River, Mingde Reservoir which intercepts Laotianliao River, a tributary of Houlong River, Dapu Reservoir which intercepts Emei River, a tributary of Zhonggang River, Jiantan Reservoir which intercepts water from Nangang River, and the Pazigang Reservoir which intercepts Houlong River. The rivers are located to the west of the Central Mountain Range, are short, steep and affected by the terrain and uneven seasonal rainfall. During droughts, the water sources are insufficient or even dry up completely. In the rainy season, the rivers overflow and inundate fields or damage irrigation structures, with frequent disasters. Among the irrigation water sources under the jurisdiction of the office, those for the irrigation areas of Mingde and Dapu Reservoir are more stable (Pazigang Reservoir was built to work in concert with Mingde Reservoir depending on the flow of Houlong River). There are also temporary weirs constructed along rivers. The irrigation water from the weirs fluctuates according to the water level and river flow, which is extremely unstable. In addition to implementing intermittent and non-normal irrigation depending on the water level, irrigation operations also pump groundwater as a supplementary water source when water is in short supply.