It definitely might, water chemistry changes extraction so much there are coffee nerds who add tablets to distilled water to get the right composition to brew with.
Whatever your thoughts on that is, distilled water is not optimal if you want to extract coffee.
That was my understanding, as well. I can only report to you what I observed.
Maybe something present in the tapwater allows more oil to be drawn out?
It definitely might, water chemistry changes extraction so much there are coffee nerds who add tablets to distilled water to get the right composition to brew with. Whatever your thoughts on that is, distilled water is not optimal if you want to extract coffee.
The filter type also changes the oil content, for example paper filters absorb much more oil than metal filters