Detroit sold about $1.8 billion in bonds tied to its water-and-sewer system on Tuesday, marking a key part of the city's efforts to improve its finances since filing for bankruptcy last year, The Wall Street Journal reported yesterday. Proceeds will be used to buy back existing debt and make improvements to the water-and-sewer system, which also serves surrounding communities. The system is currently operated as a city department and the debt deal could save the city millions of dollars, in part, through lower interest rates. Bankers on Tuesday's debt deal, led by Citigroup Inc., received enough demand for the bonds to lower some yields slightly throughout the day. A 2023 bond offered a yield of 3.24 percent and a 2037 bond offered a yield of 4.52 percent. Many of the bonds, to be paid back from water and sewer revenues, carried insurance.