Ppm and tap water

You can buy any drinking water you want honestly. But you would have to test the ppm starting point. Then add your nutrients. pH at the end. I use my sink water, it comes out at 125ppm, I let it sit for 24 hours. I add my nutrients to where I want the ppm at ( depends on plant stage ). Then I pH adjust it to where I want it. I've always done it this way and works out nicely. This can apply for soil and hydro. Hydroponics will take less nutrients.