dfk41 There are a couple of points here that I think could benefit from some context…
dfk41 I appreciate that depending on where you are will affect these figures and possibly taste. I find my own tap water fine to drink, as is the RO water I produce.
The taste of water for drinking has little relationship to the taste of coffee once it is brewed. Many brands and regions provide water that people love to drink, but are way too hard & high in alkalinity to make good tasting coffee. Let’s say someone’s water is hard at 500ppm, brewed coffee is often around 15,000ppm, espresso maybe 100,000ppm, just as an illustration. The make up of the water certainly affects the way we perceive coffee flavour (plus tea and soft drinks), due to chemical reactions between the beverage & minerals in the water, but the ‘taste of the water’ itself will be overwhelmed.
dfk41 People have told me that using pure RO water in my machine can be very harmful to the insides.
Water purification is a question of degrees & application. RO is excellent at greatly reducing contaminants and minerals in water, but if we take a reasonable definition of pure water as being less than 006ppm (parts per million), RO does not produce pure water. This is only usually the case where DI (de-ionising) filters are used, following the RO membrane, to polish the water and remove what’s left over after the RO membrane has done the heavy lifting.
You can get water much purer than this, at a cost, some scientific processes need type 1 pure water, which is so pure that it doesn’t easily conduct electricity!
Counter top RO, that doesn’t feed its waste water straight down the drain, but recirculates instead, will still produce soft water when used in a hard water area, but the water produced there (60-90ppm) may still be close to the ppm of your specific, slightly hard, tap water.