Can I say "this water" or "that furniture" ? If I can, what does it mean?
I'm not an English teacher but I speak English better than my native language so here goes. Using "this water" would simply be you referring to the water you are talking about, usually I think "this water" would be followed by some sort of adjective describing the water, for example:("is clear", "is murky", "is tasty").
The same goes for that furniture, of course pieces of furniture have names so you would be specifically pointing out a piece of furniture here. You would also be describing it and using an adjective on it based on what you see/think about it, for example: ("is old", "is broken", "is big").
And yes you can say "this water" and "this furniture", however I think it should be followed up with an adjective, otherwise it would not make sense to simply say "this water" or "this furniture" on it's own.