Because what’s in your cup is mostly what comes out of your tap
There’s a quiet truth in specialty coffee that many home brewers overlook: great espresso doesn’t start with coffee—it starts with water.
At The Roasting Party, we spend countless hours obsessing over sourcing, roasting, and dialing in the perfect double ristretto. But none of that matters if the water you’re brewing with is off. Whether you're pulling shots on your Linea Mini at home or using an AeroPress for your morning ritual, water plays an enormous role in how your coffee tastes, how your equipment performs, and ultimately, how satisfying your cup will be.
So what kind of water should you be using for espresso? Let’s dive in.
Why Water Quality Matters
Water makes up more than 90% of your espresso. It's the invisible ingredient that carries all the flavour notes from your coffee grounds into the cup—everything from stone fruit and citrus to chocolate and hazelnut.
But water is more than just a vehicle. It’s an active player in extraction. The right water will highlight origin characteristics and roast development. The wrong water will mute acidity, accentuate bitterness, or even flatten the cup completely.
More critically, poor water can slowly kill your machine. High levels of calcium and magnesium lead to scale build-up, damaging boilers and group heads—especially in home machines that aren’t descaled regularly.
So, What Makes Water 'Good' for Espresso?
Ideal brewing water strikes a delicate balance between purity and mineral content. It should:
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Be free of chlorine, odours, or off flavours
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Have moderate hardness (so minerals assist extraction without damaging equipment)
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Be neutral in pH—not too acidic, not too alkaline
For espresso, here are the rough parameters most specialty cafés and roasters aim for:
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Total Dissolved Solids (TDS): 75–150 ppm
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Calcium Hardness: 30–70 ppm
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Alkalinity: 40–70 ppm
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pH: 6.5–7.5
These aren’t just numbers—they’re the difference between a flat ristretto and one that sings.
Tap Water: The Wild Card
If you’re using straight tap water, you’re gambling. In the UK especially, water quality varies massively by region. In hard water areas like London, scale build-up and mineral overload are common. In softer areas, water may lack the structure needed to extract properly.
Tap water might be technically safe, but it’s rarely ideal for specialty coffee. At best, it dulls flavour. At worst, it damages your machine.
Filtered Water: Your Daily Upgrade
The easiest improvement you can make to your espresso is switching to filtered water. A countertop filter jug (like Brita or Peak) removes chlorine and some mineral content, while preserving enough structure for effective extraction.
For many home brewers, this is the perfect balance—accessible, affordable, and effective. Your espresso will taste cleaner, sweeter, and more expressive. And your machine will thank you too.
Distilled or RO Water? A Word of Caution
You might think ultra-pure water like distilled or reverse osmosis (RO) is ideal, but it’s actually too clean. Without any minerals at all, water can’t grab onto the flavour compounds in your coffee grounds. The result? Under-extracted, thin, and lifeless espresso.
The only exception is if you’re remineralising your water—adding a tailored mineral profile back into distilled water. Which brings us to…
Third Wave Water and Custom Mineral Blends
For the purists and coffee nerds among us, products like Third Wave Water allow you to control exactly what’s in your brew water. These mineral packets, when mixed with distilled water, create a precise profile optimised for espresso or filter brewing.
The result? Maximum flavour clarity, predictable extraction, and consistency across brews. If you’re chasing the kind of shot you’d get at a top-tier Aussie café—this is the closest you’ll get at home.
What We Use at The Roasting Party
In our roastery and cafés, we obsess over water quality as much as we do about roast profiles. Our milky drinks are all built on a double ristretto pulled with meticulously filtered water—allowing the espresso to cut through the milk without bitterness or muddiness.
For black coffees—whether espresso or filter—water plays a more direct role. It shapes clarity, acidity, and mouthfeel. That’s why we ensure a consistent mineral profile for every cup we serve or send out into the world.
The Bottom Line
If you're putting top-quality, ethically sourced, meticulously roasted beans into your portafilter, don’t let average water be your bottleneck. Whether you’re chasing the perfect double ristretto for a flat white, or brewing a clean, expressive filter from a single origin, great water is non-negotiable.
Start with filtered water. Get curious about mineral content. And don’t be afraid to experiment. Because at the end of the day, great coffee is about control—and water is one of the biggest levers you've got.
