If you've ever tried making ice at home, you've probably noticed that the ice you've made is significantly more cloudy than the ice that's served in restaurants. You might've even noticed that the cloudy ice also melts way faster than the clear ice.
To put it simply, that cloudy appearance is caused by impurities and tiny air bubbles within the ice. These impurities and air bubbles will cause the ice cube to cool down faster and thus also melt faster. If you want homemade clear ice, you should try using distilled water. If you want to take it a step further, you can even boil the water once or twice. Next wait for the water to cool down and pour it into your molds. Then cover your molds with something like plastic wrap. Next just place your "creation" into the freezer. Last but not least, go to a local restaurant and ask for a cup of ice.