Hi,

I've been using deionized water (3 ppm) mixed with Third Wave Water packets (Classic Profile) to get a solution with a TDS of 100 - 130 ppm. I have had satisfactory results using this water to brew filter coffee for the past several months, but at the moment I'm looking to move away from it. I've been thinking of using my unfiltered tap water, so I'm looking to hear some opinions on the viability of it.

Here's the information I have for my kitchen tap water:
TDS: ~50 ppm
KH: 2 dkh (tested with API aquarium water test kit)
GH: 3 dkh (like above)

Addtionally, I have attached a photo of the relevant page of the water quality inspection report from the water company where I live. The relevant rows are row 4 (pH level) and row 7 (detected Chlorine level). The report is dated August 21, 2021.
https://imgur.com/a/EMg5w85 (I can't post an image for some reasons, sorry)

I also did a cupping (not blind) of the same coffee with different waters today. In the cupping, I used the aforementioned Third Wave Water solution (#1), my tap water (#2) and a third different water (#3). The coffee I used is a Giling Bash-processed coffee from AEK Nauli, Lintong, Sumartra, Indonesia. From my cupping, I note that the tap water makes the coffee a little but more muted than #1. #1 expresses a higher level of acidity, more clearly discerned flavors but also a higher level of medicinal, bitter notes (as one can get from such a coffee). #2 is somewhat more muted, less bright acidity, but little to no bitterness and medicinal taste. I noted that #1 tasted like higher highs and lower lows. These are just my own opinions.

With this information, I'm looking to read some second opinions about whether I can still get good results from my tap water, or should I invest in some kind of water treatment system, or some other ways.

Additionally, even though I don't own an espresso machine right now, I'm wondering if I can buy one in the future and use my tap water with it.

I have neither the training nor the taste buds to be very opinionated about the effect of water minerals on the taste of coffee, and based on what I've read have come to believe that there is little that you can say about that with any certainty across various coffees and coffee tasters. But your tap water looks perfectly viable in terms of hardness and alkalinity numbers. Not far from what good coffee shops use in Vancouver, Seattle, Oslo, and Melbourne. You do want to remove the chlorine, which can be easily done with carbon filtration (carbon block, granular activated charcoal, etc.) Extended boiling the water (~ 15 minutes) or letting it stand open overnight even works for that.

Walnut Tree wrote:Additionally, even though I don't own an espresso machine right now, I'm wondering if I can buy one in the future and use my tap water with it.

That's a different issue, involving protecting the machine from limescale buildup or corrosion. Your water looks soft and should not give you limescale problems, but might possibly be corrosive. If you have high chloride numbers (chloride ion is a different thing than chlorine) then your water might require special treatment. Above 15 mg/L chloride ion may be enough for concern. La Marzocco's manuals often recommend using RO to remove chloride when the numbers are above 30 mg/L.