I think you need to try a few things and see what works for you as ultimately it seems to boil down artistic choice. What is the picture that you’ve got in your head that you want to try to produce?

Some colours may work better (my guess would be lighter colours), however I suspect any colour could be made to work. If you have a dark, non-reflective surface, then positioning your lights may create reflections in the water / help to instil it with a presence. With lighter colours you may be able to create a similar effect by adding some colour to one or more of your lights (blue tissue paper / gels for example)...

Having an object as part of the composition (possibly the source of the spill) may also give opportunities for showing reflections in the water to give it more presence.

Different types of paper are going to have a different effect on the water. Tissue paper is very absorbent, crate paper can have a matt finish, wrapping paper can be more water resistant but is often shiny. Having a slight pattern in the paper may help to emphasize the presence of the water if you can get it to distort the pattern. You may find that you can get a better balance between colour/reflection/absorbency by opting for card rather than paper.

As for how close, again it’s very subjective. If you zoom in all the way in the centre of the spill you may not be able to tell that it’s there. However from the same distance if you zoom out there’s a good chance you will... If your focus were the edge of the spill however you may be able to tell at both ends of the zoom... Your angle to the spill is going to impact how much water the light goes through between the camera and the surface which is going to change how visible the water appears.

It sounds like a fun project, but really I think you need to experiment a bit, try a few different options and see what is closest to the picture you’ve got in your head.

As it's water week, I did a bit of experimenting and for me, I thought darker colours with a bit of a reflective tint seemed to work the best.

This one's some water in a teflon pan. It caught the light well and showed an obvious water edge.

I shot another pan, which was much lighter with a matt finish and the water is far less obvious:

I quite lighted the effect of water on foil (the less shiny side)

But largely, I think it's more the angle that you shoot the water at that makes the edge of the 'spill' more obvious.