for me, MDMA + weed = hallucinations and dylerium (fun!). but yeah you need to watch your intake and be carefull not to drink TOO MUCH water either, bcause it'd lower the salts level in your body and you could die from that (hyponatremia). so not enough water kills you, but so does too much!
but it's usually not a problem, just taking a few sips every now and then constantly works out fine.

X = great!