Renal colic is a frequent presentation to the emergency department. Although most cases are genuine, up to 0.6% of cases are factitious, representing attempts to procure parenteral narcotic medication or rarely, to attain unnecessary investigation or invasive treatment. Urethral catherization has been recommended to procure an untampered urine sample, but is viewed as invasive. Calculi analysis has no relevance to acute management. We report a case of factitious renal colic which was definitively proven to be so using sample biochemistry to confirm a tap water sample contaminated with blood. This is diagnostically useful if tap water or normal saline is used to produce an alleged urine sample.