Does the quality of water make a difference in coffee?


Hi everyone!

What kind of water do you use for brewing your cup of coffee?

You might have heard that since most of coffee consists of water, the quality of water is important. This seems to be a reasonable statement. After all, the amount of stuff that dissolves from the coffee beans into the brewed coffee is very little in terms of weight.

This makes sense, but I was kind of skeptical, it just water right? I can kind of taste the difference between different types of water if I tasted them directly. But once it’s brewed I though the taste of the water is insignificant compared to the added material from the coffee. Honestly, I don’t have too much faith in my sense of taste yet, so I did not think I could tell the difference. So I used normal tap water for my coffee.

However, I thought I should test this out. So today I will be taste testing coffee brewed with different water sources.

Have I been wasting the potential of the coffee beans until now by brewing with tap water? Or will I not be able to tell the difference? Let’s find out.

Comparison Targets

I have prepared 3 types of water to use for the comparison.

Tap Water

This is the baseline, right? I live in Japan, and here tap water is completely drinkable. This obviously is not true in many places around the world, so it would be nice if I can take advantage of this. It is by far the easiest option.

The tap water in Japan is categorized as soft water (with an average hardness of about 60mg).

Tap water will differ wildly in different areas, so the results from my experiment may not be valid where you live.

Faucet Mount Filters Torayvino CASSETTY T600

The next option is filtered tap water.

The one I use is a faucet mounted type from Toray.


From the product website, it seems that they supply quite a few types of filters depending on what you want to filter out. The one I have is the T600 type which removes trihalomethane, chlorine and the mold odors.

I just happened to have this filter, so I did not get it for coffee brewing. But since I have it I thought I would use it. So this is the water that I have been using for the most part.

Bottled Mineral Water Irohas

The final option is a popular bottled mineral water in Japan called Irohas.

Source:Coca -Cola

According to their website, they bottle the water at 6 locations. The specific bottle I used was from Haku-shu. This is also soft water with a hardness of 27.

Brewing the coffee

I brewed identical cups with the 3 water options.

I used the HARIO SWITCH as an immersion brewer to keep a consistent technique. (Brew guide here)

I used the KASUGA BLEND beans from ROKUMEI COFFEE. Which were a pretty lightly roasted coffee with some bright acidity.

6g of coffee beans was brewed with 100g of around 97℃ water.

The look of each of the cups were identical.

The aromas was also indistinguishable.

Blind tasting

To remove as much bias as possible, I tasted each cup without knowing which is which.

I ordered them up according to which I liked best. And the result was; bottled water -> filtered water -> tap water. (seems to be a win for my sense of taste. haha)

The bottled water was quite different from the others, it had a clarity to it, and the acidity didn’t have a bad lingering to it. It was easier to feel the richness and the sweetness behind the acidity, and was clearly better than the other two cups.

The filtered and tap water had a much smaller difference. Compared to the bottled water, it had an edginess/sharpness to the acidity. It tasted much more acidic. But it wasn’t that the acidity was just amplified, it had a different sort of sourness added to it.

I tried the same blind tasting a second time. This time the order was; bottled -> tap -> filtered. I repeated a couple more times. I always had the bottled first, but filtered and tap swapped around, with the filtered winning out slightly more times.

I found while tasting that the difference in the tastes did not come from the different tastes of the water. Rather, the difference in the water seemed to alter what was dissolved from the coffee beans. (Its not that the filter and tap waters where sour on its own, they just brought out the sourness by reacting with the coffee)


In the end I can confidently say that I was wrong. The water used for brewing does have a noticeable difference.

The bottled water produced coffee that was easily distinguishable and better than the tap water or filtered water. Filtering the water does seem to have slight benefits, but not anything major. Of course, the results will depend on the tap water/filter you use.

The real question is, is the benefit of using bottled water more than the cost of buying bottled water?

My personal thoughts are that the benefits out weight the costs. So I have been using bottled water for brewing coffee ever since.

Try for yourself, and let be know what you find!