Why Water Quality is Important in Coffee Brewing

by Marcus McCombe | Jul 2, 2024

Why Water Quality Is Important in Coffee Brewing

TL;DR

Water makes up 98 to 99 percent of brewed coffee. As a result, its mineral content, pH, and purity directly shape how the final cup tastes. Furthermore, the right water enhances sweetness, acidity, and clarity, while poor water suppresses flavour or adds off-tastes. In the UK, where many areas have hard water with chlorine, filtering tap water (or using a remineralised alternative) is one of the easiest ways to improve coffee at home.

Why Water Quality Matters So Much

Water plays a critical role in brewing coffee because it is the primary solvent that extracts flavour from the grounds. Because water makes up around 98 percent of the final cup, its quality has a disproportionate impact on taste. Consequently, even the best beans, perfectly roasted and freshly ground, can taste flat or off if brewed with poor water.

To put it in perspective:

Water: 98 to 99 percent of the final brew.
Coffee solids: 1 to 2 percent of the final brew.

In other words, every flavour you taste arrives via the water. Moreover, anything in the water (chlorine, heavy metals, excess minerals) ends up in the cup with the coffee. As a result, water quality is one of the most overlooked variables in home brewing.

What Water Actually Does in the Cup

Water performs four distinct jobs in coffee brewing. Furthermore, each one affects flavour in a different way:

Flavour extraction. Water dissolves and carries soluble compounds out of the grounds. The right mineral content gives balanced extraction, bringing out the coffee’s best attributes while avoiding undesirable flavours.
Taste neutrality. Impurities and contaminants like chlorine or heavy metals can distort natural coffee flavours. As a result, clean water reveals what the coffee actually tastes like.
Consistency. High-quality water helps achieve a consistent brew. Moreover, if your water varies day to day (different temperatures, different mineral content), so will your coffee.
Equipment longevity. Good water prevents mineral buildup in coffee machines. In addition, it reduces the need for descaling and extends equipment lifespan.

For more on how mineral buildup specifically affects flavour over time, read our guide on limescale, the silent flavour changer in your coffee.

What Makes Water Ideal for Coffee

Not all water is the same. Specialty coffee benefits from water that meets specific criteria. Furthermore, the Specialty Coffee Association (SCA) has published guidelines for ideal brewing water:

1. Mineral Content

Water should contain balanced minerals, especially calcium and magnesium. Because these minerals help extract flavour compounds from the grounds, water with too few minerals (very soft water) tends to under-extract, producing thin, sour coffee. On the other hand, water with too many minerals over-extracts, producing flat or harsh coffee.

The SCA recommends:

Total Dissolved Solids (TDS): 75 to 250 parts per million, with 150 ppm as a target.
Calcium hardness: 50 to 175 ppm.
Alkalinity: around 40 ppm.

2. pH Level

Ideal water pH is slightly acidic to neutral, around 6.5 to 7.5. Furthermore, this range keeps coffee’s natural acidity in balance. As a result, the cup tastes bright without becoming sour or flat.

3. Purity

Water should be free from chlorine, heavy metals, and organic contaminants. Moreover, chlorine in particular adds a distinctive off-taste that suppresses delicate floral and fruit notes.

4. Softness

Moderately soft water is ideal. Hard water causes scale buildup in equipment and can over-extract coffee. On the other hand, very soft water (like distilled or reverse osmosis water without minerals added back) produces flat, lifeless coffee.

UK Tap Water and Coffee

UK tap water varies significantly by region. Furthermore, areas like London, the South East, and East Anglia have notoriously hard water, while parts of Scotland, Wales, and the North West have softer water. Consequently, the right approach to your brewing water depends on where you live.

Common UK tap water issues include:

Hardness. Many areas have hard water with high calcium and magnesium levels. As a result, this can lead to over-extraction and limescale buildup in coffee machines.
Chlorine. Used to disinfect water, chlorine adds an unpleasant taste to coffee. Moreover, even low concentrations suppress brightness.
Trace impurities. Tap water may contain trace amounts of organic compounds and heavy metals from old plumbing, which can affect coffee’s flavour profile.

If you live in a hard water area like Oxford, where Routes is based, filtering or remineralising water makes a noticeable difference in the cup.

How to Improve Your Brewing Water

Improving your water quality at home is straightforward. Furthermore, the right approach depends on your tap water and your budget. Here are the most effective options, in order:

Use a jug filter. A simple filter jug (Brita or similar) removes most chlorine and reduces hardness. As a result, the cup tastes cleaner and more vibrant, and equipment stays cleaner.
Use bottled water. Look for soft mineral waters with TDS around 100 to 200 ppm. Volvic and Highland Spring are common UK examples that work well for coffee.
Use a remineralised water product. Brands like Third Wave Water or Lotus Coffee Water provide sachets that dissolve in distilled or reverse osmosis water to create perfectly balanced brewing water.
Install an under-sink filter. For serious home brewers, a dedicated coffee water filter system gives consistent results day to day.
Test your water. A simple TDS meter (£10 to £20) tells you exactly what is in your water. Moreover, test strips can show pH and hardness.

For most home brewers, a jug filter is the single most cost-effective improvement. In addition, descaling your kettle, espresso machine, or moka pot regularly prevents mineral buildup from undoing the benefits.

How Water Affects Coffee Flavour

Different water profiles produce different coffee. Furthermore, understanding the relationship helps you diagnose problems with your cup:

Too soft (low TDS, low minerals). Coffee tastes thin, sharp, and sour. Moreover, brightness without sweetness or body. For more on this, read our guide on why coffee tastes sour.
Too hard (high TDS, high minerals). Coffee tastes flat, muted, or harsh. Furthermore, complexity is suppressed and bitterness can become aggressive. For more, see why coffee tastes bitter.
Chlorinated. Coffee tastes off, swimming-pool-like, with delicate aromatics suppressed. Floral and fruity notes are particularly affected.
Balanced. Coffee tastes clear, sweet, and complex, with good acidity and balanced bitterness.

If your coffee consistently tastes flat or off and you have already troubleshooted grind, temperature, and freshness, water is almost always the next thing to check.

Water for Different Brewing Methods

Different brewing methods have slightly different water needs. Moreover, getting the water right for your specific method can transform your cup:

Pour-over and filter coffee. Sensitive to water quality. Furthermore, soft, mineral-balanced water produces the cleanest, brightest cups. Volvic or filtered tap water work well.
Espresso. Less forgiving than filter. Moreover, hard water can clog group heads and produce harsh shots. Filtered or remineralised water is essential for home espresso machines.
French press. Slightly more forgiving because of the longer brew time. However, water quality still matters for flavour clarity.
Cold brew. The least sensitive to water quality, since cold extraction is gentler. As a result, even moderately hard water can produce decent results.

Brewing Better at Home with Routes

Great water reveals what specialty coffee can really do. A Routes Coffee subscription delivers freshly roasted single origins and blends to your door, so you always have great beans on hand. Furthermore, paired with filtered water and a careful brew, you can easily produce coffee at home that rivals anything from a specialty cafe.

Frequently Asked Questions

Why does water quality matter in coffee?

Water makes up 98 to 99 percent of brewed coffee. Furthermore, water acts as the solvent that extracts flavour from the grounds. As a result, the mineral content, pH, and purity of the water directly shape the final cup.

What is the best water for coffee?

The best water for coffee is filtered, slightly soft, and contains balanced minerals (especially calcium and magnesium). Moreover, the Specialty Coffee Association recommends water with a total dissolved solids (TDS) reading between 75 and 250 parts per million, and a pH between 6.5 and 7.5.

Can I use UK tap water for coffee?

UK tap water can be used, but it varies significantly by region. Many areas have hard water with high mineral content and added chlorine. As a result, filtering tap water usually improves coffee taste noticeably and protects equipment from scale buildup.

Does bottled water make better coffee?

Some bottled waters make excellent coffee, but not all. Look for soft mineral waters with low to moderate TDS (around 100 to 200 ppm). On the other hand, very soft or distilled water can produce flat, sour coffee, while heavily mineralised water often tastes muted.

Does hard water ruin coffee?

Hard water does not ruin coffee, but it can cause over-extraction and limescale buildup in equipment. Furthermore, the mineral content can mask brightness and complexity. Filtering hard water or using a remineralisation product like Third Wave Water solves both problems.

Should I use distilled or reverse osmosis water?

Not on its own. Distilled or RO water has had all minerals removed, which produces flat, sour, under-extracted coffee. However, you can add a remineralisation product (like Third Wave Water) to RO water to create ideal brewing water from scratch.