This Instructable will detail how to replace a Nalgene classic plastic lid retainer with a steel cable. I have done this to all of my water bottles because it eliminates a low chance of losing my water while rock climbing. There are other variations of this idea that I have seen. I prefer this method because it is the fastest and most forgivable.
a water bottle with a lid. Ideally this lid already has a retainer on it, but a small lip could be cut into a bottle lid without one. This will not be as secure.
Cable- I use 1/16th inch because its relatively flexible. About 18 inches does the job, 14" is the bare minimum.
Ferrules- sized for your cable, 2 of these
Something to crimp the cables- I use wire cutters
Optional: Something to cut the wire (dremel cutoff disk) , Rope sheath or cord to pad the wire
Step 1: Cut Off Useless Plastic Piece
I can pull this plastic to failure by hand, so Im not comfortable climbing with 1L of water attached only by that. Its a long shot but I dont want to get nailed by that and this is cheap and easy.
Angle whatever your cutting with across the plastic retainer. I used a pocket knife. Be careful, its easy to cut yourself. I find that pulling on the loop makes it easier to cut. Avoid cutting the top lip of the lid, that will decrease the safety margin.
When doing several of these at once I tend to use my dremel. The cutoff wheel can be lowered directly into the lip on the lid.
Step 2: Replace the Plastic
Run the steel cable through a ferrule on both sides creating a loop. Crimp the shorter side of this closed. Be careful not to close it entirely before adjusting it tight to the lid. See image. Adjust the outside edge of ferrule even with the outer edge of the lid, or until you're happy with it. It will be easier to open the bottle if the lid can spin inside this loop.
Repeat this process for the lip of the bottle. I try to leave my lids removable from the bottle for easy washing.
If you throw away the plastic remember to cut all loops on it.
Step 3: Add Padding
Add the sheath of a cord or rope to make carrying more comfortable. Also protects hands from fraying metal if the ends of your ferrules aren't cleanly cut. When finished, simply push the wire through the rope sheath. If using smaller cord, move this step ahead of the bottle side crimping.