Water Minerals Guide - Barista Basics

Water makes up around 98% of your coffee, and yet it’s often the most overlooked ingredient when brewing coffee. You can have the best grinder, freshly roasted coffee and perfect brewing technique but if your water chemistry is off, your cup won't be as good as it could be. Understanding how minerals interact with coffee is one of the deepest rabbit holes in coffee and it’s where coffee science meets real-world brewing. Water minerals in coffee is one of those practical sciences where you can literally learn the theory and taste the results.

In this guide, we’ll break down some of the Barista Basics such as: what TDS, hardness, alkalinity and PH actually mean, how they influence flavour and extraction in coffee and how baristas, cafes and home brewers can use this knowledge to brew better coffee.

What Is TDS in Water?

TDS stands for Total Dissolved Solids, the total amount of minerals dissolved in water. It’s expressed in ppm (parts per million) or mg/L and represents the combined concentration of all ions, things like calcium, magnesium, sodium, bicarbonate, sulfate and chloride.

When you measure TDS with a pen or meter, you’re not seeing what minerals are in the water just how much in total. This is useful for giving you a general idea of how hard your water is but with that being said, it's perfect to use a TDS Pen Meter when building a water recipe. By starting from 0 water mineral content (distilled water) you can add 1 mineral at a time and use the pen to confirm the TDS of that water. 

A TDS meter is a useful quality control tool for checking dilution ratios or ensuring consistency in a brewing setup. However, it’s not a measure of flavour quality by itself. Two waters can have identical TDS but taste completely different depending on their mineral composition (Which minerals are used).

A quick note I wan't to point out here, if you've been making coffees for a while you probably have already heard of TDS and that's because we use TDS to measure the dissolved solids in coffee after extracting. Unfortunately when it comes to measuring TDS in coffee you need to do this with a coffee refractometer, there are some budget friendly options available such as the DiFluid R2's but the best on the market are the VST refractometers. That being said, if you're looking to just measure the TDS in water then a TDS Pen Meter is inexpensive and can get you an accurate (enough) reading to create recipes and have an idea of your water's TDS.

Why TDS Matters for Extraction

Coffee extraction is all about balance, pulling out the right compounds from the coffee grounds in the right proportions. Minerals in water help extract flavour compounds, influence texture and determine how acidity and sweetness are perceived.

• Too low TDS (soft or low-mineral water): Leads to under-extraction, where coffee tastes thin, sharp and hollow. The water lacks the ionic strength to properly dissolve flavour compounds.
• Too high TDS (hard or mineral-heavy water): Can lead to over-extraction or muddy flavours, masking the clarity and vibrancy of coffee.

In practice, most baristas aim for brewing water with a TDS between 75-150ppm, depending on roast profile and brew method. Lighter roasts often shine with slightly higher mineral content to enhance sweetness and body, while darker roasts benefit from softer water to retain clarity.

Hardness (GH) - Calcium and Magnesium in Water

Hardness is determined mainly by the concentration of calcium (Ca2+) and magnesium (Mg2+) ions dissolved in water. These are essential minerals, they interact with coffee compounds to enhance flavour and extraction efficiency.

However, hardness as a number alone is misleading. High hardness increases the risk of scale buildup in kettles and espresso machines, while too little can result in flat-tasting brews.

From a sensory standpoint, Magnesium enhances fruitiness and complexity while the calcium tends to emphasise roundness and body in coffee.

But the ratio between them matters just as much as the total amount. Two waters can have the same hardness value yet taste completely different, depending on how much of each ion is present.

Alkalinity (KH) - The Balance

Alkalinity, also known as buffer capacity, measures how well water can resist changes in acidity. It’s mainly caused by bicarbonate (HCO3-) ions. In simple terms, alkalinity shapes how acidity feels in the cup with too little alkalinity coffee can taste sharp, sour or unbalanced. With too much alkalinity coffee tastes dull, chalk, or flat.

The sweet spot for most brewing applications is around 30-60 ppm bicarbonate. This range helps soften acidity without muting it.

Alkalinity is more relevant to flavour than hardness, since it measures a specific ion (bicarbonate) rather than a group. This makes it a more direct indicator of how the coffee’s acidity will be perceived.

PH - Understanding Acidity and Perception

pH stands for potential of hydrogen and measures how acidic or alkaline a solution is on a scale from 0 to 14.

• PH 7 = neutral
• Below 7 = acidic
• Above 7 = alkaline
• While it’s tempting to think that PH directly predicts coffee flavour, it doesn’t tell the whole story. Two waters with the same PH can taste very different because of their ionic makeup.

PH is often overvalued, It’s more useful for equipment protection than for predicting taste. Other ions, particularly magnesium and sodium, influence perceived acidity without changing PH, making it an unreliable standalone metric for sensory analysis.

Units and Conversions - ppm, mg/L, CaCO3 and Conductivity for Measuring Water

Water measurements can be confusing because different systems use different units:

• ppm = mg/L (they’re identical)
• 'as CaCO3' is a conversion standard for hardness and alkalinity
• Conductivity (µS/cm) measures how well water conducts electricity and can estimate TDS

Mixing up these units is one of the most common mistakes in coffee water discussions. For instance, 50 ppm bicarbonate ≠ 50 ppm as CaCO3, even though they look similar on paper.

Apax Lab suggests using mg/L as the standard unit because it’s universal and used by bottled and laboratory water testing. It also avoids confusion when comparing bicarbonate or magnesium levels directly.

If you’re mixing your own brewing water (using Aquacode or Apax Water Brewing Minerals), knowing which unit you’re referencing is essential to ensure accuracy and consistency.

Extraction, Balance and the Role of Minerals

Now that we’ve covered the technical side, let’s connect it back to flavour and extraction.

When hot water meets coffee grounds, minerals act like chemical bridges that attract flavour molecules out of the coffee bed. The type and balance of these ions determine what is extracted and how it tastes:

The ideal water for coffee isn’t about one perfect recipe, it’s about balance. Consistency is more important than hitting exact numbers. Once you know your base water composition, you can tweak it to suit your brew method:

• Pour Over Coffee: Aim for clarity, moderate hardness, medium alkalinity.
• Espresso: Slightly higher hardness for texture and crema.
• Immersion Brews (French Press, Cupping): Softer water to preserve brightness and aromatics.

Practical Tools for Water Control

If you’re serious about dialing in your water, you don’t need a lab, just a few key tools:

• TDS Pen Meter: Great for quick checks of consistency (but doesn’t show mineral type).
• GH/KH Test Kits: Measure hardness and alkalinity directly.
• Digital Scales: For those creating custom waters using Apax Water Brewing Minerals or Aquacode.

For most brewers, starting with a base like distilled or reverse-osmosis water and adding mineral concentrates offers the easiest way to achieve precise, repeatable results. It also eliminates variables like seasonal changes in tap water.

Why Water Science Matters for Every Brewer

Water isn’t just a brewing variable, it’s a medium of extraction. The right water allows coffee’s natural flavour to shine through, highlighting complexity and balance. The wrong water can mask or distort those same flavours.

Understanding the relationship between TDS, hardness, alkalinity and PH helps you brew coffee that’s more consistent, expressive and true to the roaster’s intent.

Whether you’re a home enthusiast experimenting with pour-over coffee or a professional café looking for quality control, learning the science of water gives you a genuine edge.

As with everything in coffee, precision meets art and water is the invisible ingredient that ties it all together.

When to Use Aquacode vs Apax Lab Water Minerals

Now that you understand how minerals influence extraction and flavour, the next step is knowing when and why to use different water mineral products. Both Aquacode and Apax Lab Water Minerals help you control your brew water precisely, but they’re designed for different kinds of brewers and goals.

Aquacode - The Ready to Use Solution

Aquacode is best for everyday brewers, travel, or anyone who wants reliable coffee water without the lab work.

Aquacode is a liquid mineral concentrate derived from deep-sea aquamarine sources. It’s perfect for those who want to improve brew quality without complex calculations. Simply dilute one sachet into 5-7 L of distilled or deionised water and you’ll have mineral water balanced for coffee brewing.

• Ideal use case: Brewing with soft or unmineralised water (e.g, Melbourne tap water or distilled).
• Best for: Home baristas, travellers, or cafes wanting consistent water without fine-tuning recipes.
• Flavour profile: Balanced and forgiving. The magnesium-heavy composition improves extraction clarity and body without pushing flavour extremes.
• Dilution flexibility: Use more concentrate (5 L dilution) for fuller body and sweetness, or more water (7-10 L dilution) for lighter, cleaner brews.

Aquacode is Recommended for:

• Pour over coffee (HARIO V60, Origami, Orea)
• Batch brew in soft-water regions
• Camping / travel setups where convenience matters
• Cafes looking to mineralise a batch of water at a time (5-7L)
• Flexibility to adjust with dilution, adding 1 stick to 4L of water will have different results to adding 1 stick to 7L of water).

Think of Aquacode as the 'set and forget' option, a scientifically balanced starting point that enhances clarity, sweetness and consistency without complexity.

Buy Aquacode Water Brewing Minerals

Apax Lab Water Minerals - The Precision Toolkit

Best for: Baristas, coffee professionals and enthusiasts who want full control over how water interacts with coffee flavour.

Developed by Simon Gautherin, Apax Lab’s Tonik, Jamm and Lylac mineral profiles are designed for blending. Each formula emphasises a different sensory outcome

Each profile can be used alone or blended depending on the coffee’s processing method, roast profile, or brewing style.

Example Recipes (from Apax Lab’s guidelines):

• Washed Process: 2.5 Tonik + 0.5 Jamm + 1 Lylac creates a bright and balanced taste.
• Natural Process: 1 Tonik + 2.5 Jamm + 0.5 Lylac results in rich, syrupy and sweet flavours.
• Light Roast: 1 Tonik + 3 Jamm + 0 Lylac will boosts sweetness while maintaining clarity in coffee.
• Dark Roast: 3 Tonik + 0 Jamm + 1 Lylac for structure and a smooth finish.

Why it works: Each concentrate targets specific mineral ratios:

• Tonik: higher magnesium for enhanced acidity and fruit clarity.
• Jamm: elevated calcium and bicarbonate for sweetness and creamy texture.
• Lylac: balanced sulfate and potassium to highlight florals and finish.

You can apply them in two ways, by brew water mineralisation (a more traditional approach) Simply add 3-4 g per litre of distilled water. This method is best for cafes or bulk brewing once you know which water recipe tastes great for your coffee.

Another alternative method is known as post-brewing mineralisation, by adding drops directly to the cup, post mineralising is a great way to test different combinations of profiles on the exact same coffee. Particularly useful for rare and expensive competition coffees where you don't have a lot of coffee to brew with. This method also creates less waste compared to brewing multiple cups of coffee with multiple brew water profiles. 

Apax Lab Recommended for:

• Coffee professionals experimenting with water science
• Competitors dialling in recipes for different coffees
• Home baristas exploring sensory differences between roasts and origins

Think of Apax Lab as the 'dialing in' option, precision ways to create water profiles for shaping flavour through chemistry, ideal for educational cafes, coffee competitions training and sensory exploration.

Buy Apax Water Minerals

Choosing the Right One for You