The 'AAA' rating on Naperville, Ill.'s waterworks and sewerage revenue refunding bonds reflects the system's: Strong service area economy exhibiting very high wealth and income levels, Strong financial operations with high levels of coverage and strong reserves, Competitive rates, Strong legal provisions, with the rate covenant and additional bonds test both set at 1.25x of net revenues, and Low debt burden with modest future debt needs. Net revenues of Naperville's combined waterworks and sewerage system secure the bonds. Naperville ('AAA' GO debt rating), in DuPage County, about 30 miles west of Chicago, Ill., is a rapidly growing community with a strong corporate presence. The city purchases water from the DuPage Water Commission, which, in turn, buys Lake Michigan water from