More than likely its tren. I haven't seen much dehydration from SERMs in clinic (other than complaints of atrophic vaginitis (vaginal dryness) hopefully this isn't a problem for you....lol).
Stimulants and caffeine will cause dehydration so that could be a factor if you are an avid coffee drinker or if you consume PWO stims/diet supps regularly.
With weight training it's advised that daily water consumption be no less than one gallon a day. I'm surprised no one has suggested taurine supps as yet.