A splash of paint, a splash of water, a splash of milk in my tea... so we can have splashes of any liquid. But we can also say a splash of color/colour, like "that scarf adds a splash of color/colour to your outfit". This is occasionally extended to ideas like a splash of style, a splash of creativity, although these are much less common. Another use of splash (that I can think of for now) is its use as a form of 'entrance'. She made a splash on the art scene when she first exhibited." The idea here (maybe) is that someone who makes a splash gets attention, ruffles the status quo and is entering something, here the 'art scene'. So it is possible that splash has a direct meaning, an extended idea and even possibly an idiomatic message. So no its use is not guaranteed to refer to the water.