A cup of brewed coffee or tea is almost entirely water. The beans or leaves contribute the flavor compounds, but the water is the solvent that pulls them out, and its own makeup affects how that happens. Two people using the same coffee, grinder and recipe can get noticeably different results simply because their tap water differs. Understanding a few basics of water chemistry can explain flavors that otherwise seem puzzling.
Water is not just water
Tap water and bottled water contain dissolved minerals and other substances. For brewing, the most important are:
- Calcium and magnesium, which make up most of what is called water hardness.
- Bicarbonate, which is the main source of alkalinity, or buffering capacity.
- Chlorine and chloramine, which are added to many municipal supplies as disinfectants.
- Total dissolved solids, a general measure of everything dissolved in the water.
Each of these influences the cup in a different way.
Hardness and extraction
Calcium and especially magnesium ions help extract flavor compounds from coffee grounds and tea leaves. Water with very little mineral content, such as distilled or reverse-osmosis water without remineralization, often produces a flat, hollow or overly sharp cup because extraction is less effective and the flavors lack structure.
Very hard water causes different problems. It can over-emphasize bitterness, and it leaves limescale in kettles and brewers. Scale builds up on heating elements and in narrow passages, which reduces performance and eventually damages equipment. Moderate hardness is usually the goal.
Alkalinity and acidity
Alkalinity is the water's ability to neutralize acids. Coffee's bright, fruity acidity is a large part of what makes a good Colombian coffee distinctive. When alkalinity is high, the bicarbonate in the water buffers those acids, and the cup can taste dull, chalky or muted. When alkalinity is very low, acidity can come across as harsh or sour.
Tea is also affected. High-alkalinity water can darken some teas and flatten their aroma, and it often contributes to the film that sometimes forms on the surface of black tea.
Chlorine and off-flavors
Chlorine and chloramine keep municipal water safe to drink, but even small amounts can leave a medicinal or swimming-pool note, and they can react with compounds in coffee and tea. Activated carbon filtration, found in many pitcher and under-sink filters, reduces chlorine and improves taste. Chloramine is more stable than chlorine and generally needs a filter designed for it; letting water stand uncovered does little to remove it.
Temperature for coffee and tea
Water temperature controls how quickly flavor dissolves. Coffee is typically brewed with water a little below boiling. Water that is too cool tends to under-extract, giving sour, thin results; water at a full boil poured directly onto fine grounds can over-extract bitter compounds.
Tea varies more by type:
- Black teas and many herbal infusions are usually brewed with water at or near boiling.
- Oolongs are often brewed with hot water somewhat below boiling, adjusted to the style.
- Green and white teas are usually brewed with noticeably cooler water, which helps avoid bitterness and preserves delicate aromas.
Our specialty tea guide discusses how these styles differ.
Practical ways to improve your water
- Taste it on its own. If the water tastes off, the cup will too.
- Use a carbon filter if your tap water has chlorine taste or odor.
- Check your local water report. Many water utilities publish hardness and alkalinity figures, which tell you whether your water is soft or hard.
- Experiment with bottled water. Brewing the same coffee with two different waters side by side is an easy way to taste the difference.
- Avoid pure distilled water for brewing unless you add minerals back.
- Descale equipment regularly if you live in a hard-water area, following the manufacturer's directions.
Some enthusiasts build their own brewing water by adding measured mineral concentrates to distilled water. It is not necessary for a good cup, but it shows how much control water gives over the final flavor.
Water and the rest of your recipe
Water is one variable among several. Grind size, ratio, brew time and freshness all interact with it. If a coffee tastes consistently flat or sour despite careful technique, water is worth investigating. Our guide to brewing Colombian coffee at home covers the other variables.
Key takeaways
- Minerals in water help extract flavor; too few or too many cause problems.
- High alkalinity mutes coffee's acidity; very low alkalinity can make it harsh.
- Carbon filtration reduces chlorine off-flavors.
- Coffee and tea each have their own temperature ranges, and teas differ by type.
- Side-by-side tasting is the simplest way to learn what your water is doing.