Ershui is bordered on the north by Tianzhong Township, to the east by Mingjian Township in Nantou County, and to the west by Xizhou Township. Its name means, literally, "Two Waters", which is a reference to the two irrigation canals constructed in the township, Babao canal 1 and 2, linking the waters from the nearby Zhuoshui River to the fertile Changhua Plain. Ershui is known for its picturesque scenery and the nearby Bagua Mountain Range, and offers many biking and hiking trails. The bulk of Ershui's population lives near its central plaza in front of the Ershui railway station, on the Western Line on the TRA's railway network.
The name Ershui (二水) was derived from its original name, Erbashui (二八水), which means, when translated literally, "Two 'Ba' Waters". This refers to Babao canal 1 and 2, which intake the water from the Choshui River and irrigates the farmlands of Changhua. The Babao canals are known as the "Mother Rivers of Changhua", spreading out in a fan-shaped distribution throughout Changhua county and creating a fertile plain for agriculture. After the Japanese takeover of Taiwan, Erbashui was renamed Ershuizhuang (二水庄), meaning "Ershui Village", and it was renamed to Ershui township after its designation as township after the arrival of the Republic of China Kuomintang in 1945.
Records of habitation at Ershui has been documented all the way back to 1621, in the Ming Dynasty. The first inhabitants of Ershuei first came from the Minnan region of mainland China to Lugang township in Changhua County, and then to the foothills of Bagua mountain range. The settlers co-existed with the native indigenous people, and began farming, irrigated by spring water from the mountains. The population at that time was roughly around 300 settlers.
After the construction of Babao canal 1 during the Qing Dynasty, the population spread outwards from the foothills of Bagua mountains towards the canal itself. Farms emerged on both sides of the canal, and this farming boom increased the population to 1700 people, or around 300 households. With the construction of the Erbazi passenger and freight station, local businesses emerged on 1 km of the stationfront street, which was accelerated by the formal construction of the TRA Ershui station in 1918. Finally, the construction of a pineapple canning plant in 1932 began an economic boom for Ershui, making it the most prosperous town in the Choshui River region at the time.
A popular spot for tourists and locals alike is the nearby Songboling Recreational Area. The recreational area consists of hiking trails in the Bagua Mountain range, and stretches from Ershuei township into Tianzhong township to the north of it, as well as Mingjian township in Nantou.
The various trails in Songboling, known for their beauty and breathtaking scenery, are also known for the rock macaque monkeys which inhabit the woods along the trails. The population of these macaque monkeys have boomed after tourists began feeding them. However, the local rock macaque preservation society has urged people not to feed them, since it reduces their ability to forage on their own, and overpopulation can also cause starvation.
The Ershui Station was established in 1918. The Ershui station is on the TRA Western Line, and it is the transfer station for the TRA Branch Jiji Line railroad operated by the TRA. It is designated as a second-tier train station in the TRA system.