The Romans had a trick to produce ice in the desert. It relys upon the very low (i.e. below freezing) temperature's you can get at night in a desert enviroment. What you do is: 1) Dig a deep pit. 6' or more. Once you get so far down the temperature stablises at around 50° F or so. 2) line your pit with a generious amount of straw. 3) At dusk put your container of water in the straw, leaving the top open. 4) Leave alone untill just before dawn. 5) Just before dawn, cover it over, with plenty of straw. More the better. 6) cover the top of the pit with something very reflective ( the Romans used a polished shield or two.) Repeat over one, two or three nights untill ice forms.