  We synthesized powder samples of Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O changing
the volume of the water in the hydration process, then investigated their
superconducting properties,. It was proved that the volume of water is one of
key parameters to obtain a single phase of Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O
with good superconducting properties. The transition temperature, $T_{c}$, of
the sample changed gradually while it was stored in the atmosphere of 70%
humidity. Superconducting behavior under high magnetic field was very sensitive
to $T_{c}$. $H_{c2}$ of a high quality sample with high $T_{c}$ seemed very
high.
