On a recent trip I also I tried to reduce waste and take a water bottle with me. I took an empty 20-oz Rubbermaid bottle in my carry-on. I cleared security and then filled it from a water fountain in the waiting area. I purchased a 1 liter bottle of water at one of the concessions before boarding. I was able to use the larger bottle to refill the smaller bottle which was easier to drink from and keep in the pocket in font of me. The Rubbermaid bottle also had markings to measure the amount of water so I could mix in an instant drink packet if I wanted something other than just water. It worked out very well. If I had had a layover I could refill both. On my return flight I purchased another large water bottle after clearing security for my return trip. I was able to use the 20-oz bottle throughout my trip reducing the amount of cups and bottles I might have elsewised used.
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