Consider this: a cup of black coffee is approximately 98% water. That remaining 2% is everything we care about—the acids, sugars, aromatics, and oils extracted from roasted coffee beans. Yet despite water being the overwhelming majority of what we drink, most home baristas give it barely a passing thought. This is a significant oversight. Water quality affects both the flavour of your coffee and the longevity of your machine. Understanding water chemistry can transform your brewing and protect your investment.
The Role of Minerals in Extraction
Water isn't just H2O. Tap water contains dissolved minerals, primarily calcium and magnesium, along with bicarbonates, chlorides, and sulfates in varying concentrations depending on your location. These minerals aren't passive passengers—they actively participate in extraction.
Magnesium and calcium ions bind to flavour compounds in coffee, helping to pull them into solution. Water that's too soft (lacking minerals) produces flat, underwhelming coffee because it can't efficiently extract flavour. Research by Christopher Hendon and Maxwell Colonna-Dashwood demonstrated that magnesium is particularly effective at extracting fruity, acidic compounds, while calcium tends to bring out heavier, more muted notes.
But there's a balance. Excessively hard water—water with too many dissolved minerals—causes its own problems. High mineral content can over-extract certain compounds while blocking others, resulting in muddy, harsh, or unbalanced flavour. It also deposits scale inside your machine, eventually causing serious mechanical issues.
Water hardness is typically measured in parts per million (ppm) or German degrees (°dH). The Specialty Coffee Association recommends 50-175 ppm total hardness for brewing coffee. Many Australian cities have water in the 50-200 ppm range, though some areas have significantly harder or softer water.
Total Dissolved Solids (TDS)
Total Dissolved Solids, or TDS, measures everything dissolved in water—minerals, salts, metals, and organic matter. It's related to hardness but not identical. The SCA recommends water with 75-250 ppm TDS, with a target of 150 ppm. Inexpensive TDS meters are widely available and give you a quick snapshot of your water's mineral content.
Very low TDS water (under 50 ppm) typically indicates soft water that may struggle with extraction. Very high TDS (over 300 ppm) suggests hard water that could cause scaling and off-flavours. However, TDS alone doesn't tell you everything—the specific composition of those dissolved solids matters too.
The Scale Problem
For coffee machine owners, scale is the enemy. When water containing calcium and magnesium is heated, these minerals precipitate out of solution and deposit on hot surfaces. Inside your coffee machine, this means scale building up on heating elements, inside boilers, in water lines, and in valves and flow restrictors.
The consequences of scale buildup are serious:
- Reduced heating efficiency: Scale insulates heating elements, meaning they work harder to heat water, increasing energy consumption and wear
- Temperature instability: Scale affects heat transfer, making it harder to maintain consistent brewing temperatures
- Restricted water flow: Scale narrows passages and can completely block small orifices like jet restrictors
- Premature failure: Severe scale buildup can cause heating elements to overheat and fail, boilers to crack, and valves to stick
Watch for these indicators that scale may be affecting your machine: longer heating times, inconsistent brew temperatures, reduced steam power, white deposits visible in the water tank, and grinding or clicking noises from the pump working harder than usual.
Australian Water Considerations
Australia's water quality varies significantly by region. Melbourne's water, sourced from protected mountain catchments, is relatively soft (around 10-50 ppm hardness) and generally excellent for coffee. Sydney's water is slightly harder but still within acceptable ranges. Brisbane and Perth tend toward harder water that may require filtration for optimal results and machine protection.
Adelaide deserves special mention—the city has some of Australia's hardest tap water, often exceeding 300 ppm hardness. Adelaide coffee lovers should treat water seriously, both for taste and machine protection. Regional areas fed by bore water or tank water face their own unique considerations.
Contact your local water authority for specific data about your supply, or test your water yourself using inexpensive test strips or a TDS meter.
Filtration Options
If your water isn't ideal for coffee, filtration can help. Several approaches are available, each with advantages and limitations.
Activated Carbon Filters
Carbon filters (like those in standard Brita jugs) remove chlorine, sediment, and some organic compounds that affect taste. They make water taste cleaner and can improve coffee flavour by removing off-flavours. However, standard carbon filters don't significantly reduce hardness or change mineral content. They're a good starting point but not a complete solution for hard water areas.
Ion Exchange Filters
Ion exchange filters swap calcium and magnesium ions for sodium or hydrogen ions, effectively softening water. Many in-tank coffee machine filters use this technology. They reduce scale formation effectively but can alter water's mineral balance in ways that affect extraction. Some ion exchange filters can actually make water too soft for optimal coffee brewing.
Reverse Osmosis Systems
RO systems force water through a semipermeable membrane, removing almost all dissolved minerals. The result is essentially pure water—which sounds good but isn't ideal for coffee. Pure RO water produces flat, dull coffee and can actually damage some machine components designed for mineral-containing water. If using RO water, you'll need to remineralise it for best results.
Third Wave Water and Mineral Packets
Products like Third Wave Water provide precisely measured mineral packets designed to be added to distilled or RO water. This approach gives you complete control over your water's mineral profile. It's more effort than other solutions but produces consistently excellent results. Many competition baristas use custom-mixed water for precisely this reason.
For most Australian home baristas, a quality carbon filter plus regular descaling is sufficient. If you're in a hard water area like Adelaide, consider an ion exchange filter or switch to filtered/remineralised water. Test your filtered water to ensure it's in the 75-175 ppm TDS range.
The pH Factor
Water pH affects extraction and final cup taste. Neutral pH is 7; below 7 is acidic, above 7 is alkaline. The SCA recommends brewing water with a pH between 6.5 and 7.5. Slightly alkaline water (pH 7-7.5) tends to produce sweeter, more rounded coffee by buffering some of coffee's natural acidity. Acidic water can produce overly bright, sharp results.
Most Australian tap water falls within acceptable pH ranges, but if you're noticing consistently harsh or flat results despite good technique and fresh beans, pH could be worth investigating.
Chlorine and Chloramine
Australian water utilities add chlorine or chloramine to disinfect water supplies. While safe to drink, these chemicals can impart off-flavours to coffee—that classic "pool water" taste. Chlorine dissipates fairly quickly; leaving water in an open container overnight reduces chlorine levels significantly. Chloramine is more stable and requires carbon filtration to remove effectively.
If your coffee has an unusual chemical or medicinal taste, chlorine or chloramine is a likely culprit. A simple carbon filter solves this problem.
Practical Water Recipes
For those wanting precise control, here's a simple DIY approach to creating excellent brewing water:
- Start with distilled or reverse osmosis water
- Add minerals using food-grade Epsom salt (magnesium sulfate) and baking soda (sodium bicarbonate)
- A common recipe: 1.5 grams Epsom salt + 0.5 grams baking soda per gallon of water
- Mix thoroughly and let stand before use
This produces water with approximately 50 ppm magnesium hardness and 40 ppm alkalinity—well within SCA recommendations. Adjust ratios to taste. Document what works for you and your beans.
When experimenting with water recipes, change only one variable at a time. Make a batch of water, use it for a week, and note how your coffee tastes. Small adjustments can make noticeable differences, but you need consistent testing to identify what works.
Protecting Your Machine
Regardless of what water you use, regular descaling protects your machine. Even with filtered water, some mineral content remains and will accumulate over time. Follow your manufacturer's recommended descaling schedule—typically every one to three months depending on water hardness and usage volume.
Use a descaler formulated for coffee machines. Citric acid-based descalers are effective and relatively gentle. Avoid using vinegar—it's less effective, leaves residual taste, and the acetic acid can damage rubber seals and gaskets over time.
The Bottom Line
Water quality is the most overlooked variable in home coffee brewing, yet it's also one of the most impactful. Spending time understanding your water—testing it, filtering it appropriately, and potentially customising it—pays dividends in cup quality and machine longevity. You've invested in good beans and good equipment; give them the water they deserve.
Start by testing your current tap water. Address any obvious issues like chlorine or extreme hardness. Then experiment mindfully, documenting results until you find what works for your palate and your brewing style. Your coffee will thank you.