I've had the same Camelbak bladder for several years. After each use, I empty it, roll it up and put it in a baggie, then put it in the freezer. I get it out just before I ride. I only use water in it, and so far, this procedure has worked well. No funny taste or unfunny organisms. By the way, some of my friends freeze their bladders partially filled with water, eliminating the need for ice cubes. I tried it a couple times, but the slab of ice felt like a board on my back. Here in Phoenix, I fill the bladder as full as I can with ice, then add water to fill in the gaps. It stays cold for hours.