וַתֹּ֖אמֶר שְׁתֵ֣ה אֲדֹנִ֑י וַתְּמַהֵ֗ר וַתֹּ֧רֶד כַּדָּ֛הּ עַל־יָדָ֖הּ וַתַּשְׁקֵֽהוּ׃
Ia berkata, “Minumlah, tuanku.” Lalu ia segera menurunkan buyungnya ke tangannya dan memberinya minum.
Or HaChaim
ותאמר שתה אדוני, She said: "drink my lord, etc." Instead of letting Eliezer merely sip a little water, the girl offered that he drink freely, as much as he wanted. She did not want him to have to use his hand to drink out of, but she lowered the jug to make it more convenient for him. The word ותשקהו, means that not only did Eliezer not have to lift the jug to his lips but she placed it so that he did not even have to tilt it. She brought the jug to the level of his mouth.
Radak
ותאמר שתה אדוני, the Torah records this detail in order to tell us of Rivkah’s good manners; although she did not know of the stranger’s social status she addressed him as “my lord.” She was very prompt and actually let him drink directly from her hand.