Water is 98% of the cup
Coffee extracts into water, and water chemistry gates which compounds dissolve: heavy hardness mutes brightness; chlorine adds its own flavor; distilled water under-extracts (no minerals to bind). The cup you blame on the beans is often the tap.
The cheap fixes
A carbon filter (pitcher or inline) removes chlorine — the single biggest fix for municipal water. Third-wave-style mineral packets (or a pinch of mineral concentrate) turn distilled or RO water into repeatable brew water. Boiling-and-cooling alone fixes nothing chemical; the filter does the work.
The test
Brew the same coffee with filtered vs tap water side by side once — the difference converts more coffee drinkers than any article. Then fix what the test reveals: filter for chlorine, mineral-adjust for flatness, and stop blaming the roast for the reservoir.