Growing your own starter is an elementary project than can become complicated if your water is compromised in any way. If you’re connected to a municipal water supply that’s heavy on chlorine, for example, or if you have a water softener. On the other extreme a relatively “dirty” water supply can introduce organisms that will out-compete your yeast and prevent a sturdy culture from developing. Here at the pastry house we have a water softener, which rules out the kitchen tap. I therefore use distilled water in a jug. Since feeding your culture with tap water is ideal, if only from a cost standpoint, I’d try one using that first. If nothing happens after four or five days, begin another using the bottled stuff.