A technique of utilizing waste as an interwell tracer. The waste includes pharmaceutical, personal care product (PPCP) waste or nanoplastic (NP) waste, or both. The system and method includes injecting an injection fluid including water and the waste at an injection well into a subterranean formation, producing produced fluid including water at a production well from the subterranean formation, measuring concentration of the waste in the produced fluid, and comparing the concentration of the waste in the produced fluid with the concentration of the waste in the injection fluid.