Having the water poured as a result of human action: [1]
The water must come on to one’s hand as a direct result of human action. [This comes to exclude dipping one’s hand in a vessel[2], or having an animal pour the water over one’s hands[3], or placing one’s hands under a waterfall.] This applies even Bedieved. [Thus if one is unable to wash as the result of human action a blessing may not be said over the washing. See Halacha 7A and Halacha 13.]
[1] Siddur Seder Netilah; 159:14 and Seder Netila 15 regarding washing for bread; Implied also from Basra 4:1
Ruling of Admur in Kama: In Kama 4:2 Admur rules: “The water does not have to touch a person due to the action of a human.”
Other Opinions: The Michaber 4:7 rules that initially one is to be careful to follow all the laws that apply when washing for bread. The Rama 4:7; M”B 4:17 rule that Bedieved one does not need human action involved in the pouring, as so rules Admur in Kama ibid. The M”A 4:3 rules that one may even say a blessing on such a washing. The Kaf Hachaim 4:10 brings many Poskim that rule a blessing may not be recited and so concludes Kaf Hachaim being that Safek Brachos Lihakel.
[2] See 159:17 and Halacha 13A!
[3] Siddur Seder Netilah states “power of a human” this excludes animals. In 159:20 regarding washing for bread Admur records a dispute in this matter. In Seder Netila 15 Admur writes “human power”.