All other factors being equal, ice melts faster in water than it does in air. As ice melts in air, the liquid that forms around the ice acts as an insulator, slowing down the melting of the ice. This does not occur if the ice is submerged in water.
The insulating effect of melted water around the ice may be of negligible value if the temperature of the air surrounding the ice is higher than the temperature of the water used for comparison. Higher temperatures can cause the ice to melt faster in either environment. Air currents may also speed up the melting of ice.