The Hartford-New Britain area includes the metropolitan areas of Hartford and New Britain and parts of several adjoining towns. Water used in the area is withdrawn from the principal streams and aquifers at an average rate of 463.5 mgd (million gallons per day). Sufficient water is available from these sources to meet present requirements and those for many years to come, although local shortages may develop in some areas as the result of problems of distribution and treatment. About 98 percent of all water used in 1957 was from surface sources. More than 425 mgd was required by industry, and about 23 mgd was for domestic water supply. The Farmington River upstream from Collinsville is the chief source of water for public supply in the Hartford-New Britain area, whereas the Connecticut River is the chief source of water for industry. An average of about 40 mgd is withdrawn from the upper Farmington River for public supply, and about 404 mgd is withdrawn by industry from the Connecticut River for nonconsumptive use and returned directly to the stream.

The Connecticut River is the source of the largest quantity of water in the area. The flow of the stream at Thompsonville may be expected to equal or exceed about 2,000 mgd 95 percent of the time, and the flow should not be less than this amount for periods longer than 12 days. The flow below Thompsonville is increased by additions from the Scantic, Farmington, Park, and Hockanum Rivers and from numerous smaller tributary streams. The available streamflow data for the aforementioned rivers have been summarized graphically in the report.

The chemical quality of water in the Connecticut River is good, except for short periods when the iron concentration is high. In addition to the removal of iron some other treatment may be necessary if water from the Connecticut River is used for special purposes. The chemical quality of the tributary streams is good, except the quality of the Park River, which is poor. Thus the Connecticut River in the vicinity of Hartford offers an almost unlimited source of water of good chemical quality to the Hartford, New Britain area. The Connecticut River and many of its tributaries, however, are polluted to some degree, and the cost of treatment for pollution and of delivery of water to the area presents an economic problem in the further development of these sources.

The Hartford-New Britain area in the vicinity of Hartford has been plagued by floods since the time of its settlement. Most of the damage to property and loss of life in the Hartford area has been caused by flooding of the Connecticut and Park Rivers. Floods have occurred on the Connecticut River and its tributaries in every month of the year, but the most severe floods occur in the spring and fall. The most devastating flood on the Connecticut River occurred on March 21, 1986, when the stage at Hartford reached 37.0 feet above mean sea level. The maximum flood on the Park River occurred on August 19, 1955, when the stage reached 43.5 feet above mean sea level. Floods on the other tributaries have been frequent and some have been large, but damage has not been as great because the streams flow mostly through rural areas.

Small to moderate supplies of water suitable for domestic use and for small municipalities and industries are available from wells in the Hartford-New Britain area. Moderate supplies are obtainable from five definable sand-and-gravel aquifers and from widespread consolidated sedimentary rocks. Yields to individual wells range from 15 to 400 gpm (gallons per minute) for wells penetrating sand and gravel and from 1 to 578 gpm for wells penetrating consolidated sedimentary rocks. Sand and gravel deposits bordering the Connecticut River downstream from Rocky Hill afford the greatest potential for the development of large supplies of ground water. Small supplies ranging from 1 to 40 gpm are obtainable from glacial till and from consolidated crystalline rocks.