I got the opportunity to review one of these babies. Oh MAN. I had never used a water filler in the sandbag before. I don't know if the water bladder is something you could make at home or not? I use USB and their bladder. My 1st three workouts with it and thoughts are HERE if you're interested. Theirs is definitely leak proof and made to fit their bags. Anyone else use a water filler? photo (5).jpg