Demystifying Water for Coffee

By Scott Rao

Republished by ST. DION Coffee with permission.

Demystifying Water for Coffee

Water can be a confusing topic. As I have mentioned in The Professional Barista’s Handbook and Everything But Espresso, “alkalinity” and “alkaline” mean different things. Machine manufacturers tend to focus on preventing scale, but are generally less familiar with the water chemistry that produces the best flavor—or how to balance flavor with machine protection.

The coffee industry’s historical focus on total dissolved solids (TDS) has also created the mistaken belief that an acceptable TDS automatically means water is ideal for brewing.

I’ll do my best to simplify the discussion.

The most important points are:

Alkalinity is the single most important factor affecting coffee flavor.

Always test your water before choosing a treatment system.

Water should be optimized for both flavor and scale prevention, especially in commercial settings.

Understanding Water Chemistry

TDS (Total Dissolved Solids)

TDS measures how much material is dissolved in water. While industry recommendations have traditionally suggested 100–150 ppm, TDS alone tells us very little about whether water is suitable for coffee.

General Hardness (GH)

General hardness reflects dissolved calcium, magnesium, and iron. GH may influence both flavor and scaling risk, but there is still little agreement on the ideal hardness level or calcium-to-magnesium ratio.

pH

pH measures acidity on a scale from 1–14.

Despite coffee’s reputation, brewed coffee (around pH 5) is only mildly acidic. Water pH itself is not especially important for brewing because alkalinity has a much greater influence on the acidity perceived in the cup.

Alkaline vs. Alkalinity (KH)

These are not the same thing.

Alkaline simply means water has a pH above 7.

Alkalinity (also called bicarbonate, buffer, or carbonate hardness) measures water’s resistance to becoming more acidic.

This is by far the most important water characteristic for coffee.

Higher alkalinity suppresses acidity in the cup, while lower alkalinity allows acidity to become more pronounced.

For lightly roasted, well-developed coffees, my personal preference is an alkalinity of 30–40 ppm.

Water for Home Brewing

If you’re brewing at home, several good options are available.

Review your local municipal water report.

Choose bottled water with suitable alkalinity.

Blend distilled water with minerals or products such as Lotus Water Drops.

If your tap water is already suitable, a simple carbon filter may be all you need.

If your water is hard or highly alkaline, products such as the Peak Water pitcher may help.

Water for Commercial Coffee Bars

Commercial cafés face the additional challenge of protecting expensive equipment from scale.

Machine manufacturers understandably prioritize scale prevention, but they may not recommend water that produces the best flavor.

A useful tool for estimating scale risk is the Langelier Saturation Index (LSI).

Today, many cafés use reverse-osmosis systems with blending valves. These systems remove most dissolved minerals before blending a controlled amount of filtered tap water back into the supply.

For example, if your tap water measures:

80 TDS

60 GH

60 KH

…and your target alkalinity is 30 KH, blending approximately 55% RO water with 45% filtered tap water will achieve that goal.

However, reverse osmosis is not appropriate everywhere.

Cities with naturally soft water, such as New York, often require only sediment and carbon filtration.

Test, Don’t Guess

Before selecting any water treatment system, I always recommend obtaining a laboratory water analysis.

A professional water test is inexpensive compared to the long-term costs of choosing the wrong filtration system.

At Prodigal, our water’s alkalinity is slightly above my preferred range, but close enough that we simply use sediment and carbon filtration rather than installing a reverse-osmosis system.

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Originally written by Scott Rao. Republished by ST. DION Coffee with permission.