It was considered at a time however we keep this system because it can be used for destructive purposes by griefers.
As Xeadin explains,
This is something that we do consider, but there are the few instances where players can use water as a tool for griefing (it destroys redstone, rail tracks, torches, etc.), so we'd have to be sure that who we're dealing with has the intentions to do good and to provide for the server.
If you need water, do not hesitate to ask any trusted or mod. I'm pretty sure at least one can help you with placing water. If you are curious how to be a trusted, please refer to the tips found in this thread
here.
