Here in the Austin area, the pH of tap water is 9.5. Zowee. Lake water is 8.5, but they kick the pH up to precipitate out minerals, so the water tastes better. Over the years, I've had trouble rooting in water for propagation. You know, plunk a stem in water and wait for roots to form. Turns out pH>8.5 is actually destructive to roots, and also inhibits nutrient takeup. It's called alkaline stress. Hydroponic users always keep their water slightly acidic. So why do things grow well in our soil irrigated with our tap water? Because our soil buffers whatever acidic or alkaline liquids are dumped on it to make, for me, pH 7.8. So, from now on, I'm using distilled water (or rain water) for rooting. The lesson is to be aware of your tap water pH when you're using it to root. In Texas, distilled water is free. You just catch the condensate from your a/c in the summer.