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Abstract: An explosion yielding a blast wave can cause catastrophic damage to people and property. To mitigate damage from such an event, a number of investigators have proposed the use of water in various configurations. In this investigation, an unconfined free-flowing water-sheet, with an approximate thickness of 0.3 cm, is experimentally examined using an explosively driven shock tube at three different standoff distances. The results show that the water-sheet mitigates the initial peak overpressure and impulse of the blast. Further insights into the underlying physics are revealed by a numerical simulation using Sandia's CTH hydrocode. In simulations and experiments, the air behind the water sheet experiences two distinct pressure peaks. An initial pressure rise results from the passage of a low pressure shock wave (M ≈ 1) through the intact sheet and into the air downstream of the water sheet. Following this, the water sheet breaks apart due to an increase in pressure on the forward surface caused by the buildup of the subsonic detonation products. Passage of the detonation products after breakup results in a second rise in pressure behind the water-sheet. In simulations, an initial perturbation of the water sheet is shown to affect the breaku