Does Water Quality Affect Your Coffee? (Yes, a Lot)

Here's a question most coffee drinkers never ask: what's in your water? It might not seem like it matters, but consider this — your brewed coffee is roughly 98% water. The other 2% is the dissolved coffee compounds that give it flavour. So the quality of that 98% has an enormous impact on how your cup tastes.

If you've ever made coffee with the same beans, the same method, and the same grind, but in a different location — say, at a friend's house or on holiday — and thought it tasted completely different, water quality is almost certainly the reason.

What's Actually in Your Water?

Tap water isn't just H₂O. It contains dissolved minerals (mainly calcium and magnesium), chlorine or chloramine (used for disinfection), and sometimes trace amounts of other compounds depending on your region and the age of your pipes.

The mineral content of your water is measured as Total Dissolved Solids (TDS) and expressed in parts per million (ppm). Water hardness — the amount of calcium and magnesium — is the factor that affects coffee the most.

In New Zealand, water quality varies significantly by region. Some areas have very soft water (low mineral content), while others — particularly in Canterbury and parts of the Waikato — have harder water with higher mineral levels.

How Minerals Affect Extraction

Here's where the chemistry gets interesting. The minerals in your water don't just dilute your coffee — they actively participate in the extraction process. Calcium and magnesium ions bind to flavour compounds in the coffee and help pull them into solution.

Too few minerals (soft water or distilled): Under-extracts the coffee. You'll get a flat, dull cup that lacks body and complexity. The water can't grab enough flavour compounds from the grounds.

Too many minerals (hard water): Over-extracts certain compounds, particularly the bitter and chalky ones. Hard water can also leave scale buildup in your kettle and espresso machine, which affects performance and longevity.

The sweet spot: The Specialty Coffee Association recommends water with a TDS of 75–250 ppm (ideal around 150 ppm) and a calcium hardness of 50–175 ppm. You don't need to measure this precisely at home — just knowing the general principle helps you make better choices.

The Chlorine Problem

Even if your water's mineral content is fine, chlorine can ruin your coffee. Chlorine is added to municipal water supplies to kill bacteria, and it's very effective at that job. But it also adds a chemical, swimming-pool-like off-flavour that no amount of good beans can overcome.

The good news is that chlorine is relatively easy to remove. A simple activated carbon filter (like a Brita jug) eliminates most of the chlorine and noticeably improves the taste of both your water and your coffee. It's one of the cheapest upgrades you can make to your brew setup.

What About Distilled or Reverse Osmosis Water?

If soft water under-extracts and hard water over-extracts, you might think the solution is to start with perfectly pure water and add minerals back in. And technically, you'd be right — that's exactly what some competition baristas do.

But for home brewing, distilled or reverse osmosis (RO) water creates its own problems. With almost zero mineral content, it produces a noticeably flat, lifeless cup. It can also be more corrosive to metal components in espresso machines.

Unless you're prepared to add mineral packets back into your water (which is a real thing in the specialty coffee world), distilled and RO water aren't great choices for everyday brewing.

The Simplest Fix: Use a Filter Jug

For the vast majority of home brewers in New Zealand, the easiest and most effective water upgrade is a basic filter jug. A Brita or similar activated carbon filter will:

Remove chlorine — eliminating chemical off-flavours immediately.
Reduce excess minerals — bringing hard water closer to the ideal range.
Improve taste — you'll notice the difference in both the water itself and your coffee.

A filter jug costs around $20–30 and replacement filters last about a month. For the improvement it makes to your daily coffee, it's arguably the best value-for-money upgrade in your whole setup.

Other Tips for Better Water

Always use fresh water. Don't reboil water that's been sitting in your kettle — it's lost dissolved oxygen and can taste flat. Fill your kettle fresh each time.

Let the tap run briefly first. If your tap hasn't been used for a while, let the water run for a few seconds before filling your kettle. This flushes any water that's been sitting in the pipes.

Don't use hot tap water. Hot water from the tap may have picked up minerals and contaminants from your hot water cylinder. Always start with cold water and heat it in the kettle.

Keep your kettle clean. If you notice white scale buildup inside your kettle, clean it regularly with a descaling solution or a mix of water and white vinegar. Scale buildup changes the water's mineral balance and can flake off into your cup.

It's a Bigger Deal Than You Think

Water quality is one of those variables that's easy to overlook because it's invisible. You can spend good money on great beans, grind them perfectly, and nail your brew technique — and still end up with a mediocre cup because your water isn't up to the task.

A $25 filter jug and fresh, cold water every time you brew. That's all it takes to make sure the 98% of your coffee that isn't coffee is working in your favour instead of against it.

Pair Great Water with Great Beans

Once your water is sorted, the beans are the next piece of the puzzle. All our coffee is roasted to order and shipped fresh. Browse our full range and taste the difference that quality beans and quality water make together.