I'm basically just sharing more than looking for the answer....but found it interesting enough to experiment.
I live on a different public water supply than where I work, so keep this in mind, but have identical coffee makers at home and at the office.
At work, I can make some killer Ethiopian Yirgacheffe. I've found 2 different roasting levels and both work very well at the office. A lighter one that lends more fruitiness and a slightly darker one (just before the beans turn oily) that imparts a mellow roasty flavor. It's a big hit here at the office. My 12 cups go quickly.
At home, I do everything the same, and I can NOT come close to the goodness that I get at the office. At home, we have an under-the-sink filter system and the water itself comes out very good. At work, I use unfiltered tap water. I have even gone as far as taking water from work and trying that at home with very little difference.
I have not swapped coffee makers yet (although same model). But one more thought might be wall voltage variance that has the water at different temperatures....or simply difference in QC from the factory on these coffee makers.
But I do find it strange that the quality of the final product could be so different.
Rick aka BeerAngel