Is it permissible to pour water while reciting the beginning of Surat Ya-Sin to ward off people's evil, by analogy with the action of the Prophet, peace and blessings be upon him, of throwing dust on the heads of the disbelievers while reciting Ya-Sin?

The analogy mentioned is incorrect. The story of scattering dust on the heads of the people is not comparable to merely pouring water in a certain place. Whoever fears the evil of someone should seek Allah’s help, recite the authentic supplications, and repel the evildoer’s harm with good deeds.