1) There are many, many countries where tap water is not potable. Don't gargle with it when showering, and you'll be fine. 2) Assuming you're in a climate whe

1) There are many, many countries where tap water is not potable. Don't gargle with it when showering, and you'll be fine. 2) Assuming you're in a climate where this makes sense, the easiest source of non-potable water is to simply collect rainwater, so you don't really need a grid for this. In the other direction, use of "grey water" (domestic non-sewage wastewater) for purposes like irrigation is also increasingly common.