The pH will of course vary with the water source. Seawater normally has pH value between 7.8 and 8.3 and has a good buffering capacity due to the available free bicarbonate. There is normally no need for pH adjustment. The only exception being when re-using water to a great extent.
For fresh surface water, whether river or lake, the pH will be highly dependent on the ground characteristics and whether the catchment area is exposed to acid rain. Normal pH values are between 4 and 8.5. Groundwater has a more stable pH, but the buffering capacity can be reduced and values between 5.5 and 8.5 are common. If there islimestone rock in the catchment area the pH will be high, while the pH of water coming from marshy areas can be low. The alkalinity of the different sources can vary from below 10 mg/l CaCO3 in soft freshwater to several hundred of mg/l CaCO3 in seawater and hard freshwater.
