Water levels, locations, depths, and aquifers tapped are given for 115 observation wells. Tabulated data include extremes of water levels for 1983 and for the period of record, pumpage of most major groundwater users in the State, and quality data on selected wells. The largest reported user of groundwater , the city of Lansing, pumped 8.1 billion gallons from the Saginaw Formation and glacial deposits. INTRODUCTION-Purpose and Scope This report makes available, through 1983, the records of water levels and related data for the principal aquifers of the State. It is written for municipalities, industries, institutions, consultants, drillers, hydrologists and other people interested in groundwater resources. Data on yield of wells, pumpage, quality of water, and trends of groundwater levels for the past 5 years are shown in the text. Many hydrographs are included to illustrate changes in water levels. Records of water levels in observation wells and records of pumpage by most major groundwater users, are given in tables 1 and 2. Distribution of observation wells is shown in figure 1. Location of wells sampled for water-quality data and years sampled are shown in figure 2. No water-quality data was obtained during 1983. Use of Data The quantity of water available from an aquifer can be determined by analysis of records of water levels and pumpage. Water-level records showing long-term effects of pumping can be used by municipalities, industries, and institutions to estimate the capacity of aquifers to meet present and future demands for water and to determine whether expansion of present supply systems for ground water is practicable. In an area where the water level is declining because of pumping, projection of future water levels indicates the depth below which well intakes should be installed. Allowing for lower water levels can extend the life of the installation. Normally, the water table fluctuates 2 to 3 feet annually and about 5 feet over a period of years. If an excavation for a basement or septic tank is made when the water table is low, good construction practices would allow for probable higher water levels in the spring. If construction is made after several years of drought, the allowance for rising water levels should be greater. If a site is at all questionable, the depth to the water table can be determined by test borings.