The kitchen roll test suggested above is probably a safe way to go.
Water would taste of water, coolant would taste sweet and bitter, if you were to touch a tiny bit of the liquid to your tongue and then spit it out, which is definitely NOT something I would recommend as you should be aware that ethylene glycol coolant is very very poisonous, and very small quantities injested can do permanent life changing damage to humans and other animals.
If it is coolant, it would be sensible to clean that spill up before any pets, children or wildlife take an interest in the puddle.