ph down will help with acidity, but there will usually still be stuff in the tap water (ppm, look it up). Honestly, it could also depend on where you live. For instance, I live in socal and my tap water is shit; I use an R/O system. Someone who lives near the mountains might have much better water. This is why if you are going to grow cannabis you should invest in a good PH/EC meter. I personally use a Hanna. Trust me, you need a meter. How expensive you decide to go is on you, just remember you get what you pay for. A good meter will tell you what PH/EC you are at and what your waters PPM levels are. You would know right away what is going on with your tap water by getting one.