Some of the phyics could be improved. For example:
Water will fall off the ledge to the right before filling the gap to the left, which is left unfilled. This minor error seems like it wouldn't be a problem, but ends up stopping a lot of potential devices players could create in the long run (and you'd be surprised how it ruins a lot of potential for players to be creative in this game).
Also when you kick a player, it would be useful if they disappear from the room instantly. Often people will need to kick because players will inhibit a certain area a creator is working on and are afk, and kicking solves nothing.
A clear all button would be good for the room creator, since rooms can become messy and than it gets really boring.
Also, more blocks will determine this game's success, and more importantly more ways the blocks can interact with other blocks to create cool features.
@Jiggmin, I recommend you check out this game for some inspiration if you plan on adding more block interactions:
http://www.notdoppler.com/frame/639.html it's a physics game that stays true to the physics of our universe, but is still pretty awesome and allows for endless fun because of the possibilities, especially when playing with people.