It's due to air in the water (a/k/a the di-hydrogen monoxide). <img src="http://www.traveltalkonline.com/forums/images/graemlins/Grin.gif" alt="" />

Take the aerator off the end of your faucet, then fill a teapot or whatever with the water, boil it, let it cool, boil it again, let it cool again, now most of the air should be out of the water.

Carefully pour it into ice cube trays, freeze, and you should have clear ice cubes. A lot of effort for clear ice cubes. <img src="http://www.traveltalkonline.com/forums/images/graemlins/Groovin.gif" alt="" />