John 4:9

The Jews typically regarded the Samaritans as unclean apostates. [Note: See Edersheim, 1:401.] Shortly after this incident the Jews made a law stating that "the daughters of the Samaritans are menstruants from their cradle" and therefore perpetually unclean. [Note: Mishnah Niddah 4:1.] The Pharisees prayed that no Samaritan would be raised in the resurrection. [Note: Wiersbe, 1:299; cf. Edersheim, 1:401.] When Jesus’ enemies wanted to insult Him, they called Him a Samaritan (John 8:48).

"The normal prejudices of the day prohibited public conversation between men and women, between Jews and Samaritans, and especially between strangers. A Jewish Rabbi would rather go thirsty than violate these proprieties." [Note: Blum, p. 285.]

This accounts for the woman’s shock at Jesus’ request. At this point she viewed Him as just a Jew. Ironically later some Jews would call Him a Samaritan (John 8:48).

"There was a trace of sarcasm in the woman’s reply, as if she meant, ’We Samaritans are the dirt under your feet until you want something; then we are good enough!" [Note: Tenney, "John," p. 54.]

John explained for his readers who were unfamiliar with Palestinian prejudices that the Jews did not use (Gr. synchrontai) the same objects as the Samaritans. [Note: D. Daube, The New Testament and Rabbinic Judaism, pp. 373-82.] This was so they could remain ceremonially clean.