they carry holy water (on kanwar) of river Ganga from Neelkanth, Gomukh or Haridwar to be poured on the Shivlinga in their hometown on the occasion of Shivratri

Kanwarias, as they're popularly called, are devotees of Lord Shiva. Dressed in Bhagva coloured clothes, they carry holy water (on kanwar) of river Ganga from Neelkanth, Gomukh or Haridwar to be poured on the Shivlinga in their hometown on the occasion of Shivratri. This journey on foot, when completed, is supposed to fulfil their wishes and endear them to Lord Shiva. 

kanwarias are so called because they carry a kanwar or pole on their shoulder with the covered water pots balanced on its two ends,