Drinking water PH is in the 6 to 8.5 range. Above 8.5 water hardness becomes great. Mash optimum PH is in the 5.0 to 5.5 range. 4.5 to 5.8 is the working PH of the main enzyme groups during the mashing process. Mash PH affects enzyme activity as well as the flavor of the wort. Malt and brewing water combine to determine PH of the mash. Gypsum insures proper mash conditions for best performance of the enzymes.

PH of local tap water,depends on the ground source;could be high(hard water)low(acidic)each of which cause problems,not healthwise. Check with your local water dept,they should be able to provide you with the necessary components of the water you are interested in. You could always use bottled water,and should be able to get an analysis of the bottled water from the manufacturer. Knowing the hardness and calcium content of water you are brewing with is important.