Fast flowing rivers are natural frigidaire's
Here are two survival tips, one of them is simply for luxery, the other to filter water of visable parts.
First up, the luxery tip. If you find a stream, a river or whatever, with rocks on the bottom, use the rocks to make a half circle, in such a way that it 'collects' water. You can put your bottles of water in there, or if you have watertight boxes, you can also keep meat in there. Fast flowing rivers are natural frigidaire's. Besides that cool water, fresh food, and achievements in bush-craft are good for your moral, a thing nescessary to survive.
If the bottom isn't rock but mud, you can still try to find rocks close to the river. To be absolutely sure that your food and water don't drift away in the river, tie a rope around them and secure the rope in the riverbank with a stick.
Second one, to filter water use coffee-filters, they're weight is negligible, and they work great.
Do you want to safely enjoy the wilderness?