Purity means a pure heart not bathing in holy waters
You do not become pure by bathing in holy rivers nor by performing rituals.
If you are pure at heart, whatever you do is pure.
If you think your food gets polluted because a person of low caste has touched it, then you must know that the water you drink has been tasted by millions of fish; the milk you drink has been tasted by the calf; the flowers you offer at the feet of the deity have been tasted by bees and butterflies.