Is it possible to give water more realistic properties? I know it's possible to make it, but I'm thinking of a way to spawn a great amount in order to flood enemy bases and clear them out.It would be a great tactical maneuver if water could be used to damage human bodies when their heads go under, and short bot bodies out on contact.

Possible, yes. Feasible? Only by taking severe liberties with the properties of water, and its representation graphically. It's just too much to calculate to be worth the effort.

Depends on how realistic you want the water to be.

For nearly perfect water with features such as swimming, pressure, waves, splash effects, bullet slowing, shimmering, air meter, dynamic reflections and even movability (like you put some in a bucket and you can move it around), then it would be a nightmare in a nightmare full of nightmares to code, not to mention how much it would LAG :/

Someone already made a water mod, but it doesn't have drowning yet.
http://forums.datarealms.com/viewtopic.php?f=61&t=28899

And I remember there was another water mod somewhere in the scene mod section which uses a simpler but more mario-world like form of water.