The processor does not and can not heat the incoming wash water. What it does is to fill up for the water jacket around the chemical tanks and then heat this water jacket until the chemicals are at the correct temperature. If you can set the incoming water temperature, you should set it to just below (say one deg C) the current processing temperature (24 deg for B&W and 38 deg for color). What is really important is that the processing starts
when the correct temperature is reached, assuming that the incoming water was colder than the target temperature. If the incoming water was too hot to begin with, the processing will start immediately, resulting in overcooked film.
Given this: It's good if you can set the incoming temperature to something close to but not higher than the processing temperature. This so that prewash and or other washes are in the same temperature range as the process as such.
If you only have access to cold water, than so be it. The process will run anyhow, without any big concerns. (A slight temp. chock between prewet/washes and the process as such.)
Just be sure that the incoming water isn't too hot. If so, wait until the water is cooler. (Probably around October or so in the northen hemisphere.

)
The only real difference in between the 1000 and the 1500 model is that the computer in the 1500 is a bit more modern. All the hardware is the same, as are most of the programmes. There is no difference in how the different models handle the temperature control of the chemicals. I.e. on my "old" ATL-1000 the temp. is controlled in both 24 and 38 deg. processes.
Then "common sense" says that if you have freezing cold incoming water there could be problems caused by the big prewash and postwash temperature difference. As B&W processes doesn't have any water bath for the processing drums, there will be an offset when the developer enters the chilled drum.
//Björn
//Björn