Well, the good news is, you have good Growth hormone! A good, high quality growth is going to make you retain some water. This effect is very individual, as some will gain 15 lbs, and others will gain 7 lbs, both while using the same dose of the same GH. I tend to hold most fluid intra muscular, while some will gain much more water sub q. Over time, your body will get used to the GH and some of the fluid will go away, making it easier to deal with. For this reason, I would start small, if I were in your situation, taking 2iu a day and see how you respond. After several wks, try to increase to 2.5iu and see what your body does. Then slowly climb the dose up from there. 

Take a look at your diet and see if there are areas that you can clean up. If you are using AAS as well, which I assume you are, they will make you more sensitive to sodium, which isn't going to help your situation. Also be sure to consume plenty of water. I suggest at least 1 gallon a day. Still even with a clean diet and lots of water, some will be more prone to major bloat! 

Another option would be to use blood pressure meds. Keep in mind that these meds can cause a great deal of side effects on their own, but some meds have less sides than others. Your best bet would be to speak to your Dr. I have had very good luck with a low dose of Norvasc, a calcuim channel blocker, known for having low side effects. 5mg ED is the dose I take. I don't use it year round. Just when my BP gets high. 

You should pick up a good BP machine, so that you can keep a closer eye on your day to day.