A cup of coffee is mostly water. The coffee dominates the flavor, but the effects of the taste, mineral content
and acidity of the underlying water can make a big difference to how much you enjoy your cup of coffee. Ideally the
clean drinking water you use to make your coffee should be neutral in acidity and taste, and be naturally fresh and
Normal tap drinking water is usually fine to use to make your coffee, and it is a taste that you will be
accustomed to. However, the properties of the drinking water you get from your tap do vary widely depending on
where you are. You may prefer to filter the water you use for your coffee making.
The desirable taste of coffee is slightly acidic, or for it to have some "verve" or life on your tongue. Tap
water that is strongly alkaline rather than neutral, such as in limestone regions, can detract from this sensation.
One solution is to compromise and use a lighter roast that may not seem so flat. You may prefer instead to use a
bottled drinking water to make a better tasting cup of coffee than the cup you will get using very alkaline tap
Some tap waters are strongly chlorinated to make them safe to drink. The chlorine taste may carry through to
your cup of coffee. Again the solution is to consider using bottled water. Alternatively you may find that using a
water filter that can reduce the chlorine taste will solve the problem for you.
You should not use distilled water to make your cup of coffee. This is because it is flat, and lacks the
minerals that give drinking water a more pleasant taste. It tends to produce a relatively bland cup of coffee.
Your water should be at a temperature a few degrees under boiling: around 95 degrees Centigrade or 200 degrees
Fahrenheit. If it is boiling you will alter the composition of the oils in the coffee, and it will not taste as
pleasant. This effect can come through as a slightly burnt flavor in the coffee. A good rule of thumb is to use the
water just before it boils, or to wait a minute or so after the bubbling of the boiling has subsided. Coffee
connoisseurs argue that using fresh water for heating is important, as water that has been boiled before can become
flat and detract from the taste.
Some methods for making coffee can lose too much of the heat in the water. Drip systems, for example, will lose
water temperature during the process.
While the coffee carafe can be heated on a hot plate, it is during the mixing of the water with the ground
coffee when the temperature is critical.
The espresso machine is designed to address this issue directly by controlling the temperature and pressure of
the water passing through the grounds.