Follow these steps to make your own!
Step 1: Use your Hot Water Bottle to make a Pattern
Lay out your water bottle on a double layer of the fabric that is laying flat with the right sides of the fabric together. Cut out a double thickness with a generous border around the bottle. You want to allow for the hems as well as any shrinkage of the fabric as its washed over the years.
Step 2: Fold Over a Hem on the Bottom
Step 3: Stitch Around the Edges
Before turning the cover right side out, I clipped the corners to make the corners cleaner when they were turned.