Cheapest I’ve found in the us is the Dunkin medium roast, but as others have said grinding it with a burr grinder (not a blade grinder) is a huge difference. You can buy a bag of beans and have them ground at some supermarkets though. True bulk for a community break room is gonna be hard. Best of luck.

There’s a bunch of deep dives on water chemistry, but I mix third wave water packets into one gallon of distilled water.

Do not use straight distilled water though. It will damage the machine and taste very very bad.

https://youtu.be/0ipvBdWaVzQ

I used this, but I’ve installed the shades pid, shades pressure gauge, and a dimmer mod so I was fairly familiar with the innards.

Consumer carbon filters don’t really remove enough hardness to be effective. For convenience I use distilled gallons and third wave espresso packets. There are cheaper methods though.

I wasn’t using the correct water, and after about two years I needed to replace my valve. After inspection my boiler was also beyond descaling and the steam valve was drippy. I replaced those parts because I could but only the solenoid valve was required. FWIW there are videos on how to clean the valve (after removing it) but they didn’t work for me.