effects of "interactive water" aka "dynamic fluids" can be acheived by a couple programs

the newest release of blender seems the simplest to use, atleast as far as a tub of water, or a glass being poured. i have not tried it for other situations such as a waterfall off a cliff, since i am used to other methods for doing that, or water dripping down a wet body since no events have lead me to trying it yet, but someone most likely will. this option is free

realflow as mentioned above, i have "heard" is good for the effects of water dripping down a wet body, just havent tried, the demo scared me away. this option is free demo, or pay

maya has dynamic fluids, and its one of those programs that would break your wallet and make it scream if you only get within 500 miles of it ;) think i saw it for either $1,500 or $15,000 MSRP, either way i wasnt looking again =P