Would sound absurd to all but the nerdiest, most dedicated, but have you considered making your own water[0]?

[0] https://www.baristahustle.com/diy-water-recipes-the-world-in...

Or just buy bottled water. If you're only doing Espressi, a 1 liter bottle can take you a long way and comes in under 1 Euro.

Very neat!