That's a lot of water. Do you think a purifier might simplify things for you? They make UV ones that destroy DNA & RNA; it takes about 90 seconds to make a bottle full of some river drinkable. I wouldn't use it to drink out of Lake Union, but the streams up in the Cascades, near where your photo was shot, are fine. And I don't think you'd go more than a bottle or two before finding somewhere to fill up ... but then I haven't biked east of Lost Lake.