Great progress has been made in the past 20 years in providing South Africans with access to domestic water supplies. Although groundwater is a valuable water resource with much potential, particularly in the rural and semi-rural areas with the biggest water supply backlogs, there is evidence that local authorities in South Africa increasingly consider it to be unreliable and difficult to exploit. A research project carried out on behalf of the Water Research Commission investigated groundwater supplies at local government level by carrying out interviews and studying national hydrogeological and demographic datasets. A more detailed case study of the groundwater supply to the town of Mahikeng was also made. More than 90% groundwater dependent, Mahikeng derives its water supplies from aquifers in the Vaalian-age Malmani Subgroup of the Chuniespoort Group to the east of the town, but declining groundwater levels threaten one of the two major sources. The study has found that operation and maintenance (O&M) of groundwater supplies is more important than primary or “physical” groundwater availability. Despite this, unreliable groundwater supplies are often seen as a deficiency of the primary resource and much effort is put into developing physical hydrogeological tools such as maps, guidelines and software. O&M includes repetitive tasks such as servicing, repairs, monitoring, ensuring pump duty cycles, testing, and so on, but O&M programmes also need to handle non-routine tasks such as breakdowns. Good O&M rests on adequate planning, staffing, budgeting, monitoring and other functions, as well as sufficient intra- and inter-organisational collaboration. Compared with resources for determining primary groundwater availability such as hydrogeological maps, there are few resources for institutionalising O&M procedures, and few guidelines for the O&M tasks themselves. As the case study of Mahikeng shows there is a consequent risk of greater expense and uncertainty unless efficient management (including O&M) of groundwater schemes is realised.