What causes fluid build up in feet and ankles?

It's a circulatory problem that can be for many different reasons. Mine was due to the fact they took a large vein out of my leg to repair the arteries around my heart, commonly known as bypass surgery. I think the BP meds had a lot to do with it too. They seemed to over prescribe tem right after the operation. I had several fights with my doctor about the side effects of the BP pills and eventually got it under control. I dropped one of them altogether with only good results, no increase in BP but much less light headedness and a reduction in the swelling of the leg they took the vein out of. My doctor seemed to be inclined to want me to take more pills because my BP was up when I was in his office compared to what I was getting for readings during normal life. I guess he didn't believe in "white coat syndrome". He had me on hydrochlorothiazide but I couldn't stand the dry mouth so we stopped that. When the leg/ankle swelling became more than I liked I decided to try it again and it got rid of the swelling completely. I figured if I took it in the morning the dry mouth wouldn't bother me as much during the day and by evening it should be dissipated somewhat so it would not be as bad during the night. It worked! Since then I found out they should have told me to take it in the morning to begin with instead of me having to figure that out for myself.