Bro, you should reconsider using AS that is likely to have a substantial impact on your BP levels (such as Test / dianabol), if you have a pre-exsisting condition. I understand your question is regarding water retention but be careful!!
As far as the water retention unless you increase the dosage of the diuretic you are using (not recommended) you are bound to begin to retain some additional water, dosage dependent. How much no one can tell you, only with trial with you find that out.
If you must go this route I would advice low dosage and make sure you use and anti-e. The anti-e can help with the water retention issue by keeping estrogen in check...