We use RO filtered water to fill a 5L container stored under the machine. No added minerals.
The water is fed to the machine by an Auto Top Off (ATO) device I designed and built.
The ATO is controlled by an ESP32 micro processor, the level is monitored with an optical sensor and a peristaltic pump keeps the DE1’s water dish at a constant level. This allowing us to make coffee for more than week between refills.
It cost about $40AUD in parts and has been running since Feb 2019 without fail.
Decent Espresso does sells a refill kit, for that reason I’ve not made plans available.