I just went out and gave these a try since I bought the same brand. They do hold just about 16 oz if you fill them to the zipper. They don't seem to leak if you treat them gently. The double zipper closure seem really tight.

Here is the rub, if you drop them, or just toss them around a bit, they will start to weep at the bottom seam corner. Tried it with two different bags. I tossed one in the sink (maybe 12 inches) and it did it. I tossed the other on the driveway from about 12 inches as well and the same thing happened in the same spot.

Net result, they look like they will work, just treat them as you would a condom water carrier---be gentle.

Bill