I just tested it online and it works. Gives 0 on non-blocking tiles, 11 in water, and 22 on blocking tiles.
edit: just tested it offline and it works also. Note: this is using the era tileset.
NPC Code:
//#CLIENTSIDE
if (created) timeout = .05;
if (timeout){
message #v(tiletype(playerx,playery));
timeout = .05;
}