I tried this also, but instead of water i just used cold milk.
My method was:
• Double shot espresso
• 1 sugar in the coffee to dissolve properly
• 2 ice cubes
• Mixed with the milk shake mixer.
The milkshake mixer makes the difference i think. Makes it a bit frothy at the top and properly mixes it all together.
The one i found was the one Mr.Cappuccino suggested. Relatively inexpensive.
looks like this:

I must admit the first sip i wasn't too keen, but in this heat it certainly grew on me fast! Definitely one for the summer!