Tropical Cambodia has a hot and humid climate where the rainfall regime has a close relationship with the monsoons, and this determines the two pronounced seasons, dry and rainy. The Cardamom range that extends from the coastal region to the southwest forms a natural barrier against the monsoon. This results in the central plain receiving little moisture during the rainy season. Since the proto-historic period, the Khmer have used ingenious hydraulic management systems to counter the natural absence of water in the Cardamom region. During the Fou-nan period systems remained relatively modest, but by the end of the 9th century, the Khmers started to develop very effective and efficient hydraulic systems allowing the development and enhancement of economic life throughout the region. At the beginning of the 12th century AD king Jayavarman VII chose the Dang Rek region as the location for the construction of his provincial city, Banteay Chhmar. At this time, the region was still not very favourable for the development of a large economic and political centre, due to the continuing complex hydrology and water management of the region. The foundation of Banteay Chhmar and the new system of land use required the development and construction of a complex hydrological management system and the ingenious use of space. This paper discusses the recent use of LiDaR and archaeology at Banteay Chhmar and the new discovery of the complex and diverse water management systems designed and built at Banteay Chhmar. This includes big water reservoirs called Ang Mebon, moats, weirs, sluiceways, spillways, ponds, canals and dykes.