This can happen for some people (especially women) who retain water severely, the doc will write a prescription, but usually it's only when you have obvious, painful edema. Bad edema can also happen in people with congestive heart failure & diabetes. I got a prescription written for water retention caused by birth control pills that didn't go away after several months since stopping the pill and yeah, I dropped like 10 lb. of water weight within a week and was down 15 lb. by the end of the month. I was peeing all the time. It also can happen to people with high blood pressure or pregnant women. For instance, pregnant women with pre-eclampsia can easily retain 20 lb. of fluid and sometimes after the delivery if the fluid retention doesn't improve on its own, the doc will write out a prescription. But, you do not want to be in a place where you need a prescription to lose the water weight. My feet and ankles and knees were so swollen it hurt me to even walk around the house (I was literally in tears it hurt me to walk more than a few steps). There can be a medical reason for retaining so much water weight, and these are the only people who need a prescription diuretic, not just because you want to lose weight but because you are retaining fluid severely with obvious edema that is affecting your quality of life. When I had to be on Lasix due to bad edema, I also had a potassium prescription I had to take.