Suggest a way to determine whether a colorless liquid is pure water or a salt solution without tasting it

One of the oldest ways, and simplest, to get salt out of water (and therefore determine if there is salt present) is just letting the water evaporate. Water placed in shallow basins is exposed to the sun and wind, and as the water evaporates, salt crystals form. If no salt crystals form, then there's no salt present.

If you want to save your water or speed up the process, you can just use a small sample of the water.

You can speed this up by heating, such as on a stove. Or you can use a distillation apparatus.

There's other methods... but this is, again, an ancient way to get salt from water...

One of my favorites:
Amazing Egg Experiments at Steve Spangler Science (http://www.stevespanglerscience.com/experiment/00000023)

One of my favorites:
Amazing Egg Experiments at Steve Spangler Science (http://www.stevespanglerscience.com/experiment/00000023)

That's a great way to simply test specific gravity.