· By Jos Whettingsteel
Perth Tap Water Is Wrecking Your Coffee. Here's the Fix.
Two people can buy the same bag of beans, weigh the same dose, use the same brewer, and end up with two different drinks. Not slightly different. Properly different.
The variable almost nobody checks is the one making up 98% of the cup. Your water.
And in Perth it is not one thing. It changes depending on which suburb you are standing in.
Perth does not have "one" tap water
The Water Corporation publishes its drinking water quality data every year. In the most recent report, covering July 2024 to June 2025, water hardness across Perth localities ranged from 2 mg/L to 220 mg/L.
That is not a rounding error. That is the softest supply in the metro being roughly a hundred times softer than the hardest.
The hardest readings sit in the northern corridor around Neerabup, Two Rocks and Yanchep, where the groundwater carries a lot more dissolved mineral. The typical figure across the network is about 77 mg/L, but a typical figure is cold comfort if you happen to live at the top end.
So when someone tells you Perth water is fine for coffee, or that Perth water is terrible for coffee, they are both half right. It depends entirely on where the tap is.
What coffee actually wants
Water needs some mineral in it. This is the bit people get backwards.
Minerals are what grab the flavour compounds out of the grounds. Strip them all out and you do not get a pure cup, you get a thin, sour, hollow one. Distilled water makes genuinely bad coffee.
Too much mineral is the other failure. The cup goes flat, chalky and dull, and every delicate thing in the coffee gets buried.
The Specialty Coffee Association put numbers on the sweet spot. Here is how Perth stacks up against them.
| Measure | Brewing target | Perth typical | Perth hardest |
|---|---|---|---|
| Dissolved solids (TDS) | 150 mg/L (75 to 250) | 373 mg/L | 564 mg/L |
| Hardness | around 68 mg/L | 77 mg/L | 220 mg/L |
Read the TDS row again. Perth's typical tap water sits above the top of the acceptable brewing range, before you get anywhere near the hard suburbs.
Hardness is the friendlier number. Around the average, Perth water is close to ideal. It is the top end that causes grief.
The bit cafes solve and you never see
Here is the thing that makes this feel unfair.
Walk into any decent cafe in Perth and there is a water filter plumbed in behind the machine. It is not optional and it is not an upgrade. The filter gets specced against the local supply, and in the harder parts of the metro it gets changed more often.
Nobody does that at home. You buy better beans, a better grinder, maybe a better machine, and you fill it from the tap without a second thought.
So the cafe version of a coffee has already had its water sorted before the beans arrive. Your kitchen version has not. Same coffee, different starting line.
The other half of it is scale. Hard water leaves mineral behind every time it is heated. That is what furs up a kettle, and it does exactly the same thing inside an espresso machine where you cannot see it. It is the single most common reason home machines die early.
What to actually do
You do not need a lab. In order of how much difference it makes per dollar:
Get a filter jug. A basic carbon filter jug from the supermarket is the highest-value change most Perth homes can make. It knocks back the chlorine taste and takes some of the mineral edge off. Cheap, immediate, no plumbing.
Do not use distilled or zero-TDS water. It sounds like the pure option. It makes flat, sour coffee, and in an espresso machine it can actually be corrosive. Skip it.
If you buy bottled, read the label. Look for something in the low hundreds for total dissolved solids. Plenty of Australian spring waters land in a sensible range. Mineral-heavy European waters are the wrong tool here.
Descale on a schedule, not on a hunch. If you are in the northern corridor, descale your kettle and machine more often than the manual says. The manual was not written for 220 mg/L.
Change one thing at a time. If you switch water, do not also switch grind and dose. You will not know what worked.
Our take
Water is the cheapest fix in coffee and the last one anybody makes.
People will spend $800 on a grinder and then brew with water that is 50% over the recommended mineral load. We understand why. Water is boring and invisible, and a grinder is neither.
But if you have ever had a bag at home that tasted flat when the same bag tasted great at a cafe, this is usually the answer. Not the beans. Not you. The water.
Try it before you blame anything else. Buy a filter jug, brew the same coffee you had yesterday, and taste them side by side. Most people get the answer in one cup.
And if the beans genuinely are the problem, that part we can help with. Our blends all carry a roast date, and the brew guide has our recipes for every method. Start with good water and they will taste the way we intended.
