Drain the water away and allow the ice to be in contact with air. Raising the temperature of water requires many times more input energy than raising the temperature of air. Also, air will flow over the exposed surface area of the block at a larger temperature differential than the melted water. This will encourage faster melting. When ice is melting in a glass of water, the temperature of the water itself remains close to 32F until the ice has melted. All of the energy being absorbed into the water from the environment is essentially going straight to phase changing the ice back to a liquid, but as mentioned above it requires far more energy to raise the temperature of water than air