Filtering your tap water
If you are unhappy with the caliber of your at-home water, the first option that you have is to filter it. The SCAA water brewing guidelines state that water should be clean, odor-free, clear with no chlorine. Pitcher filters like the Brita use activated carbon to remove some water impurities, odors as well as chlorine or chloramine if they are present. There are also faucet mounted filters of this type.
Soft or Hard Water?
While there seems to be some debate on the subject, using hard water makes a better cup of coffee than water softened with a home water softener.
Water hardness is a measure of the amount of magnesium and calcium that is dissolved in water. Water rich in these two minerals (magnesium in particular) are great at bringing out the best in coffee flavoring compounds. Replacing these minerals with sodium will produce a coffee that is flat by comparison.
Very hard water can destroy an espresso machine with scaling and thus it is a large concern in the pressurized coffee game. It has minimal impact of the equipment on a manual brewer. Regular kettle descaling and maintenance should make any scaling from hard water negligible.
Using Reverse Osmosis Water
Reverse osmosis (RO) is a process where all the minerals are taken out of the water. What is left is water that has virtually nothing in it. You would think that this would be ideal for brewing coffee, but it is not. Brewing with straight reverse osmosis water will produce a flat cup of coffee not unlike the coffee made with soft water.
Reverse osmosis water is missing all those magnesium and calcium minerals that enhance coffee flavor. There are, however, blending reverse osmosis systems that will mix back in mineral rich water. Some of these systems have the ability to customize the total dissolved solids level of your water. A reverse osmosis water blend is a viable option for great brewing water. The SCAA recommends 150 mg/L total dissolved solids.
If you do not have a reverse osmosis system with blending capabilities, you can blend the water yourself. Try different ratios of RO water to tap water and see if it improves your coffee taste (20 – 25% tap water is a good place to start).
If none of the above options are feasible or appealing to you, you can always brew your coffee with bottled water. Using bottled water is not a cut and dry issue either. Not all bottled waters are created equal, in fact, they can vary wildly in mineral content, pH and suitability for coffee.
“Bottled waters mostly come in two kinds, alkaline ones with massive mineral levels just below brackish, and acidic ones with mineral levels just above RO flatness. Very few have the intermediate hardness levels found in most municipal waters” (Schulman, 11).
Your best options for bottled water are going to be labeled drinking or spring water. Schulman recommends Crystal Geyser or Volvic. If you are buying bulk five gallon water blended RO jugs, try to locate a source that is using magnesium for adding hardness back into the water instead of calcium (this may be rather difficult).