Every cup of coffee is shaped by six brewing variables: grind size, water temperature, coffee-to-water ratio, brew time, water quality, and filter choice. This guide covers what each one does to coffee extraction, what too far in either direction tastes like, and what else needs to adjust when you change one.

Coffee is 98% water, which means water quality affects your cup more than almost any other variable. Here's why most home brewing water falls short and the simplest fix that makes an immediate, tasteable difference.