We report on a water maser survey towards a sample of 27 planetary nebulae ( PNe ) using the Robledo de Chavela and Medicina single-dish antennas , as well as the Very Large Array ( VLA ) .
Two detections have been obtained : the already known water maser emission in K 3-35 , and a new cluster of masers in IRAS 17347-3139 .
This low rate of detections is compatible with the short life-time of water molecules in PNe ( \sim 100 yr ) .
The water maser cluster at IRAS 17347-3139 are distributed on a ellipse of size \simeq 0 \farcs 2 \times 0 \farcs 1 , spatially associated with compact 1.3 cm continuum emission ( simultaneously observed with the VLA ) .
From archive VLA continuum data at 4.9 , 8.4 , and 14.9 GHz , a spectral index \alpha = 0.76 \pm 0.03 ( S _ { \nu } \propto \nu ^ { \alpha } ) is derived for this radio source , which is consistent with either a partially optically thick ionized region or with an ionized wind .
However , the latter scenario can be ruled out on mass-loss considerations , thus indicating that this source is probably a young PN .
The spatial distribution and the radial velocities of the water masers are suggestive of a rotating and expanding maser ring , tracing the innermost regions of a torus formed at the end of the AGB phase .
Given that the 1.3 cm continuum emission peak is located near one of the tips of the major axis of the ellipse of masers , we speculate on a possible binary nature of IRAS 17347-3139 , where the radio continuum emission could belong to one of the components and the water masers would be associated with a companion .