  Short-interval water level measurements using automatic water level recorder
in a deep well in an unconfined crystalline rock aquifer at the campus of NGRI,
near Hyderabad shows a cyclic fluctuation in the water levels. The observed
values clearly show the principal trend due to rainfall recharge. Spectral
analysis was carried out to evaluate correlation of the cyclic fluctuation to
the synthetic earth tides as well as groundwater withdrawal time series in the
surrounding. It was found that these fluctuations have considerably high
correlation with earth tides whereas groundwater pumping does not show any
significant correlation with water table fluctuations. It is concluded that
earth tides cause the fluctuation in the water table. These fluctuations were
hitherto unobserved during manual observations made over larger time intervals.
It indicates that the unconfined aquifer is characterised by a low porosity.
