hmm there is nothing new in the article on cactiguide that hasn't already been said/mentioned here ... The high pH of the commercial "distilled" water is a case for discussion ... I bet you anything that it is "demineralized" water and not "distilled". (Worst case the guys his pH meter is badly calibrated) If the demineralizing resins are not equally well generated then they will not perform their job and an alkaline or acid "residue" will "color" the final pH. Trust me, we've made and used tons of distilled and doubly distilled water in molecular biology and the "fresh" product is pH neutral. Upon standing it dissolves CO2 from the air and becomes acidic. There is a nice calculation on one of the US Uni sites that calculates the pH of CO2 saturated water at normal atm pressure and temp.
BTW The assumption of the writer that tap water contains CaclciumBIcarbonate is wrong. Water would be undrinkable if it were as it dissolves 166grams per liter. Water hardness causing "alkalinity" is calcium carbonate which for classic hard water is about 100 MILLIgram per liter ..
.. and a good pH meter is cheap ? not in my books, at least not if it must give a reliable pH reading.