I had the same question because my old set was a Swedish Asko stack washer and dryer that only required one water line. As it happens, my GE does heat its own water, but the installer put a Y valve in it to connect both the hot line and the cold lines of the machine to my one cold water spigot. In other words, if you have a hot and cold water line coming up to the washer you can use them. But if you don't have but a cold line up to the washer, the Y valve will take care of the installation. I believe the installer said you MUST have a water line in both inlets.
Oh, incidentally, I really am happy I purchased this set. They do everything my Asko did, plus does it quieter and with more ease and more features. GE really made a good pair of machines this time. Plus, the Bosch and LG small stack units only vent back into your room. This is a real bad situation in Florida where I live. We do not need to heat up rooms here, no matter what part of the house they are in. GE is the only one makes a dryer vent to the outside.