Urine specific gravity 1.005 may be caused by kidney failure, pyelonephritis, glomerulonephritis and so on. Urine specific gravity is the ratio of the weight of urine to the weight of the same volume of pure water under the condition of 4℃, and the normal reference range is 1.010～1.030. urine specific gravity 1.005 is the decrease of urine specific gravity. 1. Renal failure: it is a clinical syndrome caused by various reasons leading to a rapid and progressive decline in renal function in a short period of time, which may be due to excessive water intake, abnormal glomerular reabsorption function leading to excessive urinary excretion, thus leading to a decrease in specific gravity of urine. 2. Pyelonephritis: it refers to the infection caused by bacteria through the upward and bloodstream pathways, which induces inflammatory reaction, leading to abnormal glomerular reabsorption function and excessive urine excretion, thus leading to the decrease of urine specific gravity. 3. Glomerulonephritis: it refers to the impaired glomerular filtration function due to infection, disease and other reasons, resulting in hematuria, proteinuria, edema, hypertension as the main manifestations of the disease, glomerular reabsorption abnormalities lead to excessive urinary excretion, resulting in a decrease in the specific gravity of urine. Urine specific gravity of 1.005 may also be seen in renal insufficiency, uremia and other diseases, it is recommended that patients go to the hospital in a timely manner, under the guidance of the doctor for diagnosis and treatment.