I have been making my own water recipe, mainly rpavlis, with distilled water since getting my espresso machine. We recently moved into a new house and put a point of use RO system in the kitchen. I'm wondering if I can just use RO instead of making my own recipe with distilled. I don't want water that will scale and I'd like it to taste good. What is the general advice on RO? Will RO water scale, how does it taste with espresso - any need to remineralize? I'm guessing the answer is going to be "it depends" on what the RO is outputting.... But I'm looking for some generalities. I am going to do a GH KH test here eventually with a test kit that I have packed away somewhere. Until then, advice and speculation is welcome.

It depends on just how "pure" the RO water is. Water without any dissolved ions will not be conductive and won't allow your water boiler fill sensors to function properly. Also, absolutely pure water may be corrosive to some metals. Some folks also feel that coffee brewed with such water doesn't taste as good as water with some dissolved minerals, which is another reason (besides limescale prevention) that Dr. Pavlis formula is popular.

I switched from distilled to RO and use basically the same recipe. I have a basic TDS meter that reads under 10 when the cartridges are new and I'll check occasionally to see when I need to replace them. If Yu get one and things look low it would be great in my book.

I've been using RO water for years, but there's a caveat. RO systems produce water at less than 100% efficiency. For example, our water is considered "very hard", so the product water from our RO is about 12 to 25 PPM TDS, depending on the time of year. If you're using Pittsburgh city water, your product water won't be as hard as ours, because Pittsburgh water is considered only "hard". It won't be soft enough to stop triggering your fill probe; although theoretically correct, it's actually quite rare for this to happen. But, I suspect it will be too soft to have good tasting coffee. I suggest you use it as is, and then tinker with additives until you get a taste you like. I use a simple pen style TDS meter as a gauge to know whether to add a bit of bicarb to my reservoir (hardly ever do so any more, as my taste buds are 76 years old ).

I agree with others that if the RO is performing adequately, you can use it in a water recipe as if it were distilled or deionized. You should not use it as-is, both for taste and corrosivity reasons. And if it's too pure your water level sensors would not detect it.

And agree that you can check how the RO is performing with a simple conductivity 'TDS' meter.

I was previously using RO water (25 TDS) with some filtered tap to increase pH and alkalinity. I've now moved to RO + TWW. I'm not using a full packet per gallon, but I'm generally finding that my coffees are exhibiting a wider range of "good" than my previous method. I would absolutely not use straight RO due to likely low pH and alkalinity.