  Extensive airshower detection is an important issue in current astrophysics
endeavours. Surface arrays detectors are a common practice since they are easy
to handle and have a 100% duty cycle. In this work we present an experimental
study of the parameters relevant to the design of a water Cerenkov detector for
high energy airshowers. This detector is conceived as part of the surface array
of the Pierre Auger Project, which is expected to be sensitive to ultra high
energy cosmic rays. In this paper we focus our attention in the geometry of the
tank and its inner liner material, discussing pulse shapes and charge
collections.
