No. Soaked raisin water alone is not proven to reduce hypertension.
Raisins contain potassium, and diets rich in potassium-containing fruits and vegetables can support blood-pressure control. But the benefit comes from the overall eating pattern, especially a low-salt
DASH-style diet, not from raisin water specifically. The NIH notes DASH lowers blood pressure, while potassium's separate effect is difficult to isolate.
NIH potassium fact sheet
If you like it, have a small amount and eat the soaked raisins too, but do not stop prescribed BP medicine or rely on it as treatment.
Caution: Do not deliberately increase potassium through foods or supplements without medical advice if you have kidney disease or use medicines such as ACE inhibitors, ARBs, or spironolactone. The
American Heart Association guidance advises checking with a clinician in these situations.