If you have empirical evidence that God created the cold which froze the water or froze the water himself then you are correct. Otherwise, the natural forces, which can be observed, (the temperature of the air and water and the observation of the water becoming ice) would be used in this case. The empirical evidence has been in plain sight, so to speak, for a long time. You put a tray of water in your freezer and after a period of time you have ice cubes.
Have a look at this link and tell me if natural forces are responsible for the ice form...
I can and do infer design. Who better than a designer to recognize it and just as I don't need to know who a designer is when I see designed objects I don't need to infer a specific being. Remember I can as an agnostic only infer from observable evidence. In my world I design objects in 3D, I know what it takes to form not only those individual objects but also how to form multiple objects that function together as a system. As a mechanical engineer I also have a fairly good understanding of the natural environment since I must design around it daily.