Why is it advised to not carry Gangajal from Kashi

Gangajal was and is considered to be sacred and purifying, and has the capability to wash the sins and purify the soul, be it living or dead. Many believe that Gangajal has the power to help the soul attain moksha and when sprinkled around the home or a space, it can cleanse the energies that reside in it. But, Gangajal is almost always preferred only from Haridwar and not Banaras. Why? Read to know.