“I am not having adequate urine flow inspite of drinking water. What could be the problem?”

May have an enlarged prostate

You might not be making enough urine, which might be kidney disease. Is your blood pressure normal? Also, is your weight stable, or are you gaining weight which would indicate fluid overload (from not making enough urine)? The other possibility is that you may have a bladder obstruction (male would be prostate; female would be uterine or ovarian mass).
Initial studies to check for possible abnormalities would include blood studies such as creatinine and electrolytes (kidney function tests) and ultrasound of kidneys and bladder. You are wise to note these changes and have an evaluation of your kidneys and bladder.