Pani Jaisa Piyar is the story of Sana, a 25-year-old girl from Faisalabad. She has two older siblings, Hassan and Dua. Sana's family used to be wealthy and of a high social class, but this all went away after the death of her father. The family's only support now is that of Hassan, who quit school at an early age in order to support the family. Sana has been engaged to Adarsh, the son of her mother's best friend Arfa ever since she was a child. Adarsh, however, has been unaware of this engagement, as his parents thought that he needed to focus more on his education than wedding plans.
Adarsh, however, is in love with Sasha, a childhood friend of his. When he tells his parents that he wishes to marry her, they refuse, saying that he is already engaged to Sana and that he will have to leave their home if he doesn't marry her. After much deliberation, Adarsh decides that it would be best to marry Sana, as there is no point in marrying Sasha if they have no home and no money.
Back in Faisalabad, Sana's brother Hassan is taken to prison after getting into a fight with boys from the neighborhood who were making inappropriate remarks towards Sana. Hassan's best friend, Saad, who has no family of his own, takes care of the 2 sisters and their mother in Hassan's absence. Saad has already told Sana that he likes her, but has never done or said anything more on the matter as he knows that she is already engaged. Sana feels uncomfortable in his presence, but her mother, thinking that Saad will stop aiding them, makes Sana spend time with him anyway, as she believes that the only feelings Saad has towards her daughter are brotherly. Saad takes Sana out to dinner one day, and he takes Sana to his house to show her around. Sana refuses at first, but says yes after Saad insists. Saad shows Sana his room, which is decorated with pictures of her, and confesses that he is in love with her. He asks for one night with her, and rapes her when she tries to run away. He takes her back home an hour or two later, telling her that he will withdraw Hassan's court case if she tells anyone, and she complies. When Hassan is acquitted, however, Sana cannot keep the truth in much longer, and tearfully tells him everything. Hassan, in anger, chases Saad to the railway and tracks and chokes him to death, being taken back to jail soon after.
Sana's mother Nuzhat wishes to wed Sana off to Adarsh as soon as possible after this, without telling him or his family about Sana's rape. But Sana tells Adarsh's mother Arfa anyway, knowing that she will break their engagement the second she hears the news. However, Arfa, who is indebted to Nuzhat because she took Arfa's daughter Dua in and raised her as her own so that Arfa could get remarried and live a pleasant life, accepts Sana. She tells Sana that she has told Adarsh everything and that he accepts her as well.
After Sana and Adarsh's wedding, Sana brings the topic up, saying how grateful she is that Adarsh accepted her knowing everything that had happened to her. Adarsh however, is unaware of the circumstances, and flips out when Sana tells him everything. He is furious that his mother tricked him like this, and believes that Sana was not raped at all, but did everything of her own free will. He begins to treat Sana horribly, and restarts his relationship with Sasha, even going so far as to having sexual relations with her. When Sana finds out that she is pregnant, Adarsh denies any possibility that the child is his, and claims that Sana must have an abortion because he doesn't want to take care of her illegitimate child. Sana, not knowing what to after being accused of so many crimes, and still being in the aftershock of the death of her mother and hanging of her brother, attempts to commit suicide by overdose of sleeping pills. However, Arfa and Adarsh find her just minutes after the pills take effect and take her to the hospital, and there is no harm done.