They're wrong. Look up Numbers 5:17, where a ritual is being described and the text says, "[A]nd the priest shall take holy water in an earthen vessel and take some of the dust that is on the floor of the tabernacle and put it into the water."
This shows that holy water not only has a basis in the Bible, but that it has been around since the days of Moses. Holy water was used for numerous Old Testament ceremonies that involved ceremonial sprinklings and washings. Today we are not bound to perform those ceremonies, but the fact holy water was used at all proves that it is not a superstitious or invalid practice.