Is it permissible to wipe the head during ablution more than once without putting new water on the hand, given the uncertainty of the water reaching all the hair?

What is legally required in wiping the head is to wipe from the front of the head to the back, and then return to the front, based on the action of the Prophet, peace and blessings be upon him. It is not obligatory to ensure that the wiping covers all hair or that all hair is wet, because that would transform it from wiping to washing, and wiping is based on ease.