The sustainable use of groundwater from karst aquifers is key for sustainable development in the Grootfontein-Tsumeb-Otavi Subterranean Water Control Area (GTO-WCA) in Namibia. The ever-increasing demand for groundwater for irrigation purposes in the GTO-WCA and for argumentation purposes to the Central Area of Namibia has put the aquifer under pressure. Proper groundwater management is therefore required to protect this finite resource. This study assessed the sustainability of groundwater use in the GTO-WCA by assessing the behaviour of groundwater users in the GTO-WCA and by assessing the current legislation and regulatory mechanisms followed by authorities in their allocation of groundwater to the users. The results indicate that groundwater use for irrigation has increased above the sustainable safe yield for the aquifers in this area. The paper elaborates on reasons for the current state of affairs and proposes specific management solutions. Keywords: Grootfontein-Tsumeb-Otavi Subterranean Water Control Area, Sustainability, Groundwater use, Irrigation, Karst.