Is reverse osmosis water too pure for coffee?

The misconception that reverse osmosis (RO) water is "too pure" stems from a misunderstanding of its role in the brewing process. RO is not a finished product; it is a foundational tool. In its raw state, RO water lacks the magnesium, calcium, and bicarbonate buffers necessary to facilitate proper extraction. Without these minerals, water acts as a poor solvent, failing to pull the complex sugars and acids from the coffee grounds, which leads to the thin, acidic, and "hollow" cup profile often criticized by home brewers. For the coffee producer, this is a tragedy: the nuanced work of drying, fermentation, and varietal selection is effectively muted by the water's inability to carry those flavors to the palate. The professional approach, now standard in high-end cafes, is to treat RO water as a blank slate. By stripping the water of unpredictable local contaminants—such as chlorine, heavy metals, and fluctuating mineral loads—baristas can reintroduce specific mineral ratios. This allows for a level of precision that ensures the coffee tastes exactly as the producer intended, regardless of the local water supply. The goal is not to avoid purity, but to control it. By moving from the variability of tap water to a controlled RO-based system, the industry shifts the focus from fighting the water to highlighting the bean.