Knowledge of groundwater age / residence time in Okongo perched aquifer is important in understanding key issues in the evolution of groundwater, recharge rates, recharge mechanisms, resource renewability, flow rate and distribution of recharge areas. The build-up in the atmosphere of trace gases such as sulfur hexafluoride (SF6) and tritium (3H) from over a centenary ago offers a convenient way of dating groundwater up to the age of 60 years.