Good quality water bottles are great, but the lid for many of them can get lost if you remove it while camping or hiking. Tactical weblog ITS Tactical shows how to tie a handy retention strap using 24 inches of paracord.
You'll need to know how to tie a double fisherman's knot and a bowline. Make a loop and tie a double fisherman's knot. Once that's complete put the loop over the mouth of the water bottle and tighten.
This is a quick easy mod that is much better than trying to find a replacement lid for your bottle on Amazon.
How to Make a Liberty Bottle Leash for Your Lid [ITS Tactical]