A 67-year-old Queens woman was sexually assaulted in her home after she invited in a man who had asked for a glass of water, cops said.

She encountered the pervert Monday in her building in Fresh Meadows at 2 p.m. When she invited him in, he pulled a knife and forced her to perform a sex act.

Police said he is black, between 45 and 65 years old, 5-foot-9 and weighs 160 pounds. He wore black-rimmed glasses.