Amounts of water withdrawn, delivered, consumed, released, returned, and lost or gained during conveyance were determined for six communities--Rockford, Loves Park, North Park, Kankakee, Bourbonnais, and Bradley--served by the public-water systems in the Rockford and the Kankakee areas of Illinois. Water-use categories studied were commercial, industrial, domestic, and municipal uses; public supply; and sewage treatment. The availability and accuracy of water-use data are described, and water-use coefficients and methods of estimating water use are provided to improve the collection and the analysis of water-use information. Water-use data were obtained from all the water utilities and from 30 major water users in the Rockford and the Kankakee areas. Data were available for water withdrawals by water suppliers; deliveries by water suppliers to water users; returns by sewage-treatment plants and water users; releases by water users to sewers; and sewer-conveyance losses. Accuracy of the water-use data was determined from discharge measurements or reliability tests of water meters, or was estimated according to the completeness of the data. Accuracy of withdrawal and sewage-treatment-return data for the Rockford area and of withdrawal, delivery, industrial release, and sewage-treatment-return data for the Kankakee area was considered to be at least 90 percent. Where water-use data were inadequate or unavailable, various methods were used to estimate consumptive uses; releases; returns by commercial, domestic, and municipal users; and conveyance losses and gains. The methods focused on water budgeting to assure that water uses balanced. Consumptive uses were estimated by use of the consumption-budget method, the types-of-use method, consumptive-use ratios, the winter base-rate method, and the maximum lawn-watering method. The winter base-rate method provided the best domestic consumptive-use estimates, whose ratios (consumptive use from the winter base-rate method divided by deliveries and self-supply withdrawals), by community, ranged from 0.03 to 0.136 and averaged 0.068. The consumption-budget and types-of-use methods, as well as consumptive-use ratios, were used to estimate consumptive use for commercial, industrial, and municipal categories. Water budgeting was generally used to estimate releases, and conveyance losses and gains. Estimates of nonconsumptive uses by cooling systems, boilers, and lawn watering; data of deliveries to septic-system owners; and (or) water budgeting were used to estimate commercial, domestic, industrial, and municipal returns. Proportions of water use were similar in the Rockford and the Kankakee areas. Of the public-supply withdrawals in each area, about one-half was delivered for commercial and industrial uses; about one-third for domestic use; and about one-sixth for municipal use and public-supply conveyance losses.Consumptive use by all water users in the Rockford and the Kankakee areas was 13 +/- 1 percent, releases were 78 +/- 2 percent, and returns were 9 +/- 2 percent of deliveries and self-supply withdrawals. Total returns were greater than total withdrawals in the two areas because-of sewer-conveyance gains, which amounted to about 34 percent of the sewage-treatment returns for each area. Delivery rates (deliveries divided by the number of users [establishments or households]) and domestic per capita use were similar for all six communities. At a 95-percent confidence level, domestic delivery rates for each community range from 0.067 to 0.075 million gallons per household per year. Commercial delivery rates range from 0.277 to 0.535 million gallons per establishment per year. Delivery rates for all categories combined range from 0.100 to 0.192 million gallons per user per year. Domestic per capita use, which ranged from 67.2 to 71.0 gallons per day, averaged 69.2 +/- 1.1 gallons per day.