  A new Air Shower Observatory has been constructed in Buenos Aires during
1999, and commissioned and set in operation in 2000. The observatory consists
of an array of four water \v{C}erenkov detectors, enclosing a geometrical area
of $\sim$ 30.000 m$^{2}$, and is optimized for the observation of cosmic rays
in the ``knee'' energy region. The array detects $\sim$ 250 to $\sim$ 1500
showers/day, depending on the selected triggering condition. In this paper, the
design and construction of the array, and the automatic system for data
adquisition, daily calibration, and monitoring, are described. Also, the Monte
Carlo simulations performed to develop a shower database, as well as the
studies performed using the database to estimate the response and the angular
and energy resolutions of the array, are presented in detail.
