Filtered Water Versus Tap Water for Coffee

Cup with water, to its right is a question mark

My company office uses one of those single use packet Flavia coffee machines, and the resulting beverage it makes are not as good as the coffee I make at home. I got sick of it. To fuel my addiction needs I brought my own ground beans and an AeroPress to brew in. Thus, for my coffee break I would bring the apparatus to the kitchen, boil some water, pour it into the brewer, make the coffee, and enjoy.

The problem? The coffee was still mediocre; it tasted a lot more like the one the coffee machine made! Why???

Maybe… the water is the problem?

Fun fact, coffee is mostly water! Thus, the quality of the water correlates to the quality of the coffee. Conventional wisdom suggests to filter your water before using it to brew with. For context my city’s tap water is safe to drink. However, the water is hard (has dissolved minerals) and intentionally has residual chlorine. There are few ways to filter water to reduce chlorine and minerals for better tasting water. The easiest is to use a jug filter, which uses activated charcoal and ion exchange resin to capture water impurities into the filter cartridges.

When I started brewing my coffee with filtered water I noticed an improvement in taste.

Testing out the office water

At the office I have three different choices for potable water: the tap, the filtered faucet (looking at the maze of pipes under the sink, that seems to be the one the Flavia coffee machine uses), and the water cooler (which has its own filter). The water from the cooler seems to taste the best. I started using that water instead of the filtered tap and my coffee seemed to taste better since.

I wanted to be scientific about it, to prove to myself that the office coffee is subpar because of the water. Thus, I some collected water samples to use the next morning for a blind taste testing.

For the test I had 5 different samples of water:

  1. Office cooler (filtered)
  2. Office filtered faucet
  3. Office tap
  4. Home jug filtered
  5. Home tap

Keeping it simple, I chose to brew in the same mugs the coffee will be tasted from. Each mug had a label at the bottom for later identification. I grounded up 10 grams of coffee bean into each mug, ready to be hugged by freshly boiled water. The challenge was boiling the water one after the other; I couldn’t brew at the same time.

5 mugs with coffee, different water used in each

I mixed the mugs around until I long lost track of which is which. I started tasting each one by one, and took notes on how each tasted. Then, I ordered the mugs from what I interpreted to be the best to the worst. Though, I must admit they didn’t taste too different.

What shocked me, is that I rated coffee brewed with office tab and my home tap water the highest! What!? That made no sense! I must have inconsistently brewed each mug… or something…

Testing Home water

I decided to reduce the scope of my test. I focused on testing the tap versus filtered water at home.

This time using two AeroPress brewers. Into each I added 15 grams of coffee grounds. Pored 150 grams of freshly boiled water. After the brew was gently pressed into a mug I poured 50 grams of milk. I normally have my coffee with milk, and I wanted to compare it in terms of how I typically drink coffee.

Test 1

Using True North Blend Starbucks beans (that in hindsight might have been stale).

Both cups sucked, and tasted the same. I picked the worse cup out and it turned out the be tap water. It was the one that tasted marginally less gritty. Though it might have been luck I guessed the “bad” cup.

Test 2

In the second test I used Zavida Organica, which are my go to affordable commercial coffee beans.

Both cups tasted decent. A little gritty, and with a mild after taste. I could not tell the two apart; they exactly tasted the same.

Test 3

At this point I thought my filter needs to be replaced. Thus, this third test was done a with a fresh filter cartridge (Kirkland brand).

I used Caffe Borborne’s Creme Superiore roast. According to the packaging it was roasted 3 months ago in Italy.

This time the cups did taste distinctly different! One cup had a clear chocolate taffy taste note to it. The other was more bitter. Both had a bitter-ish after taste.

So, the punchline? The better tasting mug was brewed with tap water!

Test 4 and 5, NO coffee just water

Okay, forget coffee… let’s just taste the water. Two mugs, one filtered, one tap, blind test go!

First attempt

I picked filtered water as the tastier of the two. But, it was also noticeably warmer then the tap water. It was at room temperature while the tap water was still freshly cool from the tap.

Second attempt

This time I let both the tap and filtered water sit for a couple hours so that their temperature difference isn’t a factor. In the blind taste I picked out filtered water as tastier, the tap water tasted, what I can only describe as, with a faint trace of chalk while filtered water tasted more clear.

Conclusion

While it’s clear that by it self the filtered water tastes better, it makes little difference to the taste of coffee. At least for the water I have at home. Your experience may differ depending on your water’s contents. Though, none of this explains why the coffee I brewed in the office tasted subpar…

Further readings and videos on the topic

Credits

Written by Victor Efimov

Published on June 4, 2025