The pressure response during a well test provides information on well productivity and reservoir performance. To replace traditional production tests, avoiding the gas flaring and increasing operational safety, the injectivity test began to play an important role in the management of the reservoirs in these fields. Although analytical models are able to describe injection and falloff periods, variable rate models still need to be developed. This work attempts to present a variable rate approximate solution for pressure response in a water injection well. The accuracy of the proposed solution was assessed by comparison with a numerical simulator. The suggested model was also used to determine the reservoir equivalent permeability.