Bulk Buying Water in Japan

Where do y'all go to bulk buy water? Most combinis sell 2 liter bottles for ¥120 (¥223/gal or $1.44). However that seems a bit expensive over the long term since in the US for example, you can get water refills for $0.40/gal in most grocery stores and was wondering if there are better alternatives. Thank you!

by Icy-Highway-5980