The main concepts for identifying and removing barometric pressure effects in confined and unconfined aquifers are described. Although is commonly known that barometric pressure changes can effect water level readings, few articles and procedures are provided to correctly manage piezometric data. Knowing the barometric efficiency reduces errors in calculating piezometric surfaces and drawdowns in the piezometers during pumping tests. Stallman (1967) suggested furthermore, that air movement through the unsaturated zone and the attendant pressure lag, could help to better describe the aquifer properties. Rasmussen and Crawford (1997) described how barometric efficiency varyes with time in some aquifers and how to calculate the corresponding barometric response function (BRF). They also showed that this last parameter is related to the degree of aquifer confinement. Finally we present an application of the procedure in an unconfined karst aquifer located in northern Namibia (Otavi mountainland) where a set of four absolute transducers have recorded water level changes and earth tides during a 10 months period at 1 hr interval.