The dipole-bound anion of the water dimer is studied via an ab-initio approach. Two nuclear stable configurations, trans-(H2O)(2)(-) and cis-(H2O)(2)(-), are both identified on the potential energy surface of the anionic water dimer. In addition, the transition state connecting the stable trans-(H2O)(2)(-) and cis-(H2O)(2)(-) is also located. The transition barrier, relative stability and vertical detachment energies (VDEs) of these two configurations are evaluated at high electron-correlated levels of theory. Consequently, the trans-(H2O)(2)(-) is found to be unstable against electron autodetachment. The only electronic and nuclear stable species of the anionic water dimer is the cis-(H2O)(2)(-). The experimental implications of these findings are also discussed.