I think itnwas the loghtening God slayer when he developing the fire lighting abilities. 

In anycase, yes, a water user could make their water hotter or colder, and what you are describing there is juvia. But she can only make ice, when paired with Gray. And they do that unionson raid.

I don't magically think that the water dragon slayer could use ice, unless eating the properties of another dragon slayer or God slayers magic that is connected to ice