Water quality is an oft-forgotten component to brewing great coffee. A target range of 150-200 ppm (parts per million) is typically the hardness level that promotes proper and even extraction of coffee particulate.
These numbers can seem a bit arbitrary, but bottled water companies oftentimes list the mineral breakdown and Total Dissolved Solids percentage on the back of the bottle. A quick search online might also yield a resource providing such necessary information.
A more permanent at-home solution is a water filter. But water filtration can be tricky.
At Cartel, we use a reverse osmosis filtration system that effectively controls the TDS consistently. Installing a home RO system or finding a source that will be reliable is the best way to acquire high-quality water. Depending on where you live, post-tap filtrations may work. Charcoal filters, however, do not filter out chlorine or high amounts of mineral content.