The Problem With Tap Water
Most tap water in the US is either too hard (high mineral content) or too soft (treated/filtered to remove everything). Both are bad for coffee in different ways.
Hard water (over 200 ppm total dissolved solids) creates chalky, muted coffee. The excess calcium and magnesium interfere with extraction. You also get scale buildup inside your kettle and espresso machine, which shortens equipment lifespan.
Soft water (under 50 ppm) produces sour, thin coffee. Without enough minerals to bond with the flavor compounds during extraction, the good stuff stays in the grounds. Distilled water is the worst case -- it tastes dead flat and under-extracts dramatically.
The Ideal Range
The Specialty Coffee Association recommends water with 75 to 150 ppm total dissolved solids and a pH between 6.5 and 7.5. Most bottled spring waters fall close to this range. Crystal Geyser and some regional spring waters test well for coffee.
The easiest test: buy a $10 TDS meter from Amazon. Fill a glass from your tap and dip the meter in. If you are between 75 and 150 ppm, your water is fine. Below 50 or above 200, it is worth fixing.
Simple Fixes
For most people, a Brita or ZeroWater pitcher is enough. These reduce chlorine taste and bring very hard water closer to the ideal range. If your TDS is already in the right zone, a carbon filter (like a fridge filter or faucet-mounted Brita) just removes chlorine flavor without stripping minerals.
For espresso machines, consider a dedicated water softener or use a recipe like Third Wave Water. These mineral packets are added to distilled water to create a precise mineral profile optimized for coffee extraction. A single packet costs about $0.60 and makes one gallon.
The espresso machine angle matters most: hard water scales the boiler, which is expensive to repair. Soft water is corrosive to metal components. The right water protects your equipment and improves the taste.
Do Not Overthink This
If your tap water tastes clean and neutral, it is probably fine for coffee. The people who need to worry are those with well water, very hard municipal water, or reverse osmosis systems that strip everything out. For everyone else, a basic carbon filter and fresh beans will get you 95% of the way there.