Water accounts for about 95% of urine volume; the remaining 5% consists of solutes. The largest component of urine by weigh, apart from water, is urea, which is derived from normal breakdown of amino acids. Other nitrogenous wastes in urine include uric acid (an end product of nucleic acid metabolism) and creatinine (a metabolite of creatine phosphate, which stores energy for the regeneration of ATP and is found in large amounts in skeletal muscle tissue)
Normal solute constituents of urine, in order of decreasing concentration, are urea, Na+, K+,PO4 3-, SO4 2-, creatinin and uric acid. Much smaller but highly variable amounts of Ca2+, Mg2+ and HCO3- are also present in urine,
Unusually high concentrations of any solute, or the presence of abnormal substances such as blood proteins, white blood cells or bile pigments, may indicate pathology.