Can you bring water to into the theater ( From home ?)

Not officially, no.

Just put it in your bag. I would think you can't because they sell it, but nothing a bag can't hide.

Yes you can.

Honestly, I've done that before but I dont recommend it.

I've never been stopped. I often take in a bottle from home. I carry it in in place sight, out in the open in one hand. Hopefully people won't abuse (taking booze and what not in) them allowing this.

There is no law concerning such things, policy maybe, but buying "stuff" at the theaters will keep them open...it's on you...