Water levels in wells vary with the amount of recent precipitation
depending on the season and on the type and depth of well. In general, the
deeper the well, the less flucuation in the water level, the longer the
water has been in the ground, and the less impact a drought has on the
water level. Water infiltrates into permeable soil when precipitation or
snowmelt occurs. Some of this water percolates to aquifers (a soil or rock
layer of the earth which releases enough ground water to make pumping
feasible) during periods when precipitation exceeds the extraction demands
of plants or evaporative demands at the surface of the soil. These
"recharge" periods are typically from fall through late spring, although
frozen soils during the winter may greatly reduce entry and flow of water
in the soil. From late spring through early fall, the evaporative and
transpiration (referred to as "evapotranspiration") demands frequently
exceed precipitation. Consequently, water in the soil is depleted by plant
growth, and there is less flow to ground water. Hence, shallow water tables
in Connecticut are usually high in late fall, winter and spring, but are
low during the summer and early fall.

In general, wells can be divided into three categories: shallow upland,
alluvial and deep bedrock.
Shallow wells in upland areas are typical of individual homeowner wells and
may vary in depth from 10 to approximately 30 feet. These wells may be dug
or drilled into glacial till which consists of compacted mixtures of sand,
gravel, and clay sized particles. They are usually low capacity wells, with
flow rates less than 1 gallon per minute (gpm). The water level in the well
is at the level of the water table in the vicinity of the well which may
fluctuate greatly, both seasonally and with extended dry periods. The
position in the landscape, i.e. on top versus on the side or the bottom of
a hillslope also is a major factor in the both the depth to the water table
and the variation of the water table. Water taken from these wells has been
in the ground for short periods, typically on the order of months.

Alluvial wells are located in sand and gravel layers that have been
deposited by running water during the geologic past. These typically are
along larger streams in river valleys, but are found in some parts of the
state such as the central Connecticut River valley at some distance from
the current river location. These wells typically have very high
capacities, for example 100 to 1000 gpm and experience less seasonal
variation in water levels than the upland shallow wells. Water in these
systems often has been in the ground from a few days to months to a few
years and often is not greatly affected by short term drought conditions.
The flow in nearby rivers is frequently fed by water from these aquifers,
and pumping at high rates can affect the amount of flow in the stream.

Bedrock wells are drilled through overlying glacial till or alluvial areas
into bedrock. Most domestic wells in the State are bedrock wells drilled
into crystalline rock. These wells get their water from fractures (cracks
in the rock) that happen to be intersected by the well. Water levels in
these wells do not typically vary greatly by season but may be affected by
extended drought conditions. The water in the fractures may have been in
the earth from several months to many years.