My understanding is that BMI or Body Mass Index does not involve underwater weighing or anything like that. It's just a fancy way of determining whether you are too heavy for your height. My husband and I had our BMIs done for a life insurance physical exam right in our own home, and all the nurse did was take our height and our weight and plug it into a formula in a calculator. You could probably find someplace online to calculate it yourself by plugging in your height and weight numbers. Your doctor would be able to do that for you too and could probably recommend a healthy weight for you. Underwater weighing is to determine how much of your weight is fat (20% or 30% or whatever). You can also get this done (although a little less accurately) by the pinch test where someone does some measurements with a calipers on your abdomen and under your arm to see how much fat they can pinch there. Personal trainers and other fitness professionals are often trained to do this. Maybe your doctor's office could do it too.