Not sure if this has been discussed… It is my understanding that the reason Nestle’s brands of water bottles are used is because they accommodate the netcups. If it helps any, you can use a heat gun (or blow dryer) to slightly melt a water bottle to give it shape. This could increase the amount of bottle you can find and recycle. Takes about 15 seconds per bottle. I had a hard time finding 1.5 liter Nestle’s brands of water bottles. I did however find quite a few evian water bottles of the size volume, which did not have the center indent. Heat gun worked great. Hope this helps.