No one can really give you advice about this without knowing what's in your tap water. At a minimum, you need hardness and alkalinity numbers in order to make any scaling estimate, and to choose a treatment that might avoid scale buildup problems.

Having said that, if you are on the Abilene water described here: https://saveabilenewater.com/wp-content ... _web-1.pdf, you will have scale buildup problems if you don't soften that water. A fridge carbon filter won't do the job, and any system that will is going run you more than 100 bucks.

That Abilene water is especially problematic because of the 87 - 166 ppm chloride levels. This will not cause scale problems, but may cause corrosion problems. Best advice here would be to go with a reverse osmosis filtration system to remove that chloride. (Carbon filters effectively remove chlorine, chlorite, chloramine in the small levels added to disinfect the water supply, but will not filter out that chloride.)

I think your most practical option would be to repair your Flojet system and use carboys of spiked purified water under the sink. The R Pavlis water is simply distilled or RO water with 50 - 100 mg/L of potassium bicarbonate. On a 5 gallon carboy that would be about 1 - 2 gram of potassium bicarb per 5 gallon fillup. It will have a nice non-corrosive alkalinity, will deposit no scale, and most folks say that it produces fine tasting espresso.

P.S.
Summarizing the numbers in that 2017 City of Abilene report that I linked above:

Total hardness 182 - 346 ppm
Total alkalinity 111 - 127 ppm ("temporary hardness" would be roughly equal to this)
Calcium hardness 138 - 208 ppm (calculated from Ca ion)
Chlorite ion 0.9 ppm
Chloride ion 87 - 166 ppm
Sulfate ion 63 - 212 ppm
TDS 366 - 717 ppm
Conductivity 698 - 1340 umhos/cm (would read 349 - 670 ppm on typical inexpensive TDS meters)

I was hoping homeburrero might step in. He has an excellent grasp on water for espresso. The above post is very good advice regarding water for your machine. It will not harm your system and tastes good also.

As I mentioned in your other post regarding the FloJet, I would go to a more robust pump and stay with the carboys for supply and waste. With that type of pump and John Guest tubing rather than the FloJet setup you presently have you could just draw water from a one gallon store container and keep a slightly larger waste container. As long as you are not making many drinks per day (I make 2-3) the minor inconvenience of changing the jugs is minimal and you will always have fresh water at your disposal with no periodic cleaning of the carboy for the supply side. Again as I mentioned in the other post this is what I plan to do when, not if, my present FloJet fails. I should order that pump as I have likely just jinxed myself by even mentioning it failing.

To make Dr. Pavlis 10% water premix, I add 10 gr. of Pot. Bicarb to 100gr./100ml distilled water. When I change jugs of water I add 4 ml. (4gr.) of the premix to the fresh gal. of distilled water. This is not a perfect value (3.8ml/3.8gr.) but close enough for me. Easy Peasy. Of course, my coffee bar is in an area without plumbing so it is a predetermined selection to not have it on the local water system. Pot. Bicarb is cheap on Amazon for a pretty much lifetime supply at the rate I use it and I can get steam distilled water for less than a dollar a gallon at Wally World. Ultimately I suppose a treatment system could pay out if I had plumbing available but there is still maintenance required to keep the system working in the long haul so I really somewhat doubt it for the minor expenses I incur. If you are making many more drinks per day than I the cost versus payout will likely reverse.

Best of luck with whichever way you choose to proceed.