The function not associated with the human kidney is (b) Control of sugar level in blood. While the kidneys play essential roles in regulating water balance, filtering waste products like urea, and secreting various hormones involved in blood pressure regulation and red blood cell production, they are not directly involved in controlling blood sugar levels. This function primarily falls under the purview of the pancreas, which secretes hormones such as insulin and glucagon to regulate glucose metabolism. Therefore, while the kidney performs numerous vital functions, controlling blood sugar levels is not among its primary responsibilities.