I'm trying to render a splash to be like water. The material type I have selected is glass, however it either looks like white ceramic or tin foil depending on which lighting environment I give it. You can also see on the image below that where the splash is in front of the cans, it appears see through. But when the splash is away from the can, it colours in a 100% opacity so you can't see through to the background image
Does anyone have any ideas on making this look more real?
Objects use the Environment Light for reflection and refraction in glass/liquids. It looks like you have one of the more generic grey studio lights in place which is lighting and reflecting through the glass that solid gray color. I'd recommend using Match Image to create an environment light from the background image for general ambient light and reflections, then use the Sunlight to do a spotlight towards the front.
I'd also move your camera up a bit so it is looking down at the water surface instead of across it... another option is to move the splash down below the surface plan but imo moving the camera up will give better results