Mediates the transport of urea driven by a concentration gradient across the cell membranes of erythrocytes and the renal inner medullary collecting duct which is critical to the urinary concentrating mechanism (By similarity). Facilitates water transport in erythrocytes (By similarity). urea(in) = urea(out) Homotrimer; each subunit contains a pore through which urea permeates (By similarity). Identified in a complex with STOM (By similarity). Restricted to the basolateral membrane in various portions of the urothelium. Belongs to the urea transporter family.