For anyone that's interested in how to make a transition to sparkling mineral water without all the single-use plastic waste, the answer is to DIY.
Making a DIY force-carbonation rig is trivial and costs around $100 upfront: https://www.seriouseats.com/pros-cons-diy-carbonation-rig
Cloning mineral waters is also easy enough to do: https://khymos.org/2012/01/04/mineral-waters-a-la-carte/
I've been doing this for a while and have had great results. Even if you're not tee-totaling, it's still a fine investment for cocktails and DIY alcoholic seltzers.