泸 is a place-name character. It names 泸州 in Sichuan, known for its strong liquor, and an old name for a southwestern river. The line 五月渡泸 comes from Zhuge Liang's famous memorial about campaigning south.
The water radical in its three-drop left form, from 水. It marks the character as a river name, which is its original use. River-name characters regularly take this radical. It groups 泸 with 江, 河, and 湖.
