About Some Guied lines

Sir I have one question for long time in my mind WFI ( Water For Injection ) Ph limit for pharma industry is 5.5 to 7 But which Guied lines they follow For So Any one know plz tell about in deep and flowest language

The same is mentioned in the different pharmacopoeia (B.P. or I.P etc.). Under the manufacturing process of the WFI, it is clearly mentioned the limit of the pH.